materials Article
Optimization of TiC Content during Fabrication and Mechanical Properties of Ni-Ti-Al/TiC Composites Using Mixture Designs Dong-Jin Lee 1 1 2
*
ID
, Jae-Ha Park 2 and Myung-Chang Kang 1, *
Graduate School of Convergence Science, Pusan National University, Busan 46241, Korea;
[email protected] Software Division South Office, IREATECT Co., Busan 49465, Korea;
[email protected] Correspondence:
[email protected]; Tel.: +82-51-510-2361
Received: 13 May 2018; Accepted: 2 July 2018; Published: 4 July 2018
Abstract: Ni-Ti-Al alloys are highly promising materials for use in high-temperature structural materials. However, minimal research has been conducted to improve the associated mechanical properties through secondary phase addition. In this study, Ni-Ti-Al/TiC composites were fabricated at a pressure of 40 MPa and a sintering temperature of 1050 ◦ C using spark plasma sintering. The microstructure and interfacial structure were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis. Microscopic analysis revealed that TiC particles interacted with Ti and Al, resulting in the formation of Ti2 AlC, which promoted chemical metallurgical bonding between the Ni–Ti–Al alloy and TiC. Wear characteristics were measured using the wear test with a ball on disk. It was confirmed that the 40 wt % specimen had the highest hardness due to pores generated inside, but the wear amount was relatively high. The mixture design of a minitap was proceeded using hardness, bending strength, and wear loss. An optimum composition ratio of 32.16 wt % was determined using the composite desirability of the three properties. Keywords: Ni-Ti-Al/TiC; tribology behavior; TiC content optimization
spark plasma sintering;
mixture designs;
1. Introduction The potential application of Ni-Ti-Al-based alloys for use in aerospace and high-temperature structural materials is acknowledged with respect to their low density, high strength at high temperatures, and high corrosion resistance. Initial studies improved the strength of Ni-Ti-based shape memory alloys at high temperatures by preparing Ni-Ti-Al by the substitution of a small amount of Ti with Al [1,2]. Furthermore, a recent study was conducted to improve the corrosion resistance at high temperatures and prevent a deterioration in mechanical properties, in which less than 10 at% Al was used for the precipitation of the Ni2 TiAl phase and NiTi phase [3]. To improve the mechanical properties of Ni-Ti-Al-based alloys, metal elements, such as Mo, Nb, Hf, Zr, B, and Re, have been added to alloys [4–6], and these properties have also been evaluated at room temperature. For example, the refractory alloy, Mo, was added at the interface between TiAl and NiAl to improve yield strength and compression strength, and Nb was added to improve the oxidation resistance. To improve the mechanical properties at high temperature, Ni-45Ti-5Al-2Nb-1Mo alloy was prepared by adding a small amount of at% [7]. In addition, studies have been conducted to improve the compressive strength at room temperature by preparing (Ti, Al) 2 Ni and (Zr, Ti, Al) 2 Ni solid phase by adding 8 at% of Zr [8], and numerous studies have investigated methods to improve high-temperature properties [3,9,10].
Materials 2018, 11, 1133; doi:10.3390/ma11071133
www.mdpi.com/journal/materials
Materials 2018, 11, 1133
2 of 10
However, it is necessary to research the application of metal- or ceramics-based composites in extreme environments due to the development of advanced industries. Mechanical properties research has previously been limited to compressive strength tests (because these composites are high-temperature structural materials), but limited research has used room temperature to investigate the wear loss of the product or evaluate its mechanical properties. Furthermore, mechanical properties have been evaluated under limited conditions, due to the uniform composition ratio of the added materials; however, few studies have aimed to find the optimal composition ratio because composition ratio tests are expensive and time-consuming. Therefore, in this study, TiC [11,12] with various composition ratios is added to Ni-Ti-Al and sintered using identical sintering conditions in all experiments. The material properties are analyzed by measuring the microstructure, composition distribution, phase, and density; and mechanical properties, such as bending strength, hardness, and wear loss are measured and applied to the mixture design. The optimum content of TiC is obtained using the composite desirability of the mixture design. 2. Materials and Methods In this experiment, Ti (99.96%, 45 µm), Al (99.95%, 45 µm), Ni (99.9, 45 µm), and TiC (99.95%, 3 µm) were employed at the composite ratios shown in Table 1. In the chemical reaction presented in Equation (1), all of the TiC can disappear during sintering, so that the conditions were excepted the composition of TiC 10 wt %. SUS balls with diameters of 10 mm were mixed at a ball/powder ratio (BPR) of 10:1 for 10 h. Ti + Al + TiC → Ti2 AlC, (1) Table 1. Chemical composition of mixed powders (wt %). Sample
Ni
Ti
Al
TiC
Ni-Ti-Al/20 wt % TiC Ni-Ti-Al/30 wt % TiC Ni-Ti-Al/40 wt % TiC
40 35 30
36.8 32.2 27.6
3.2 2.8 2.4
20 30 40
The Ni-Ti-Al/TiC powders were charged into a graphite mold with a diameter of 30 mm, pre-formed by hand press, and then sintering using spark plasma sintering (SPS: DR. SINTER SPS-825, FUJI-SPS, Gothenburg, Japan). In the preliminary experiment, the sintered material exited from the graphite mold at a pressure of 40 MPa and at temperatures of 1100 ◦ C or higher and adhered to the disk. Therefore, sintering was subsequently conducted by maintaining the pressure at 40 MPa, the temperature elevation at 100 ◦ C/min, and the sintering temperature of 1050 ◦ C for 10 min in a vacuum atmosphere. The densities of the specimens were measured using the Archimedes method, and the average of five measured values was used to calculate the theoretical density. Relative density values were calculated using Equation (2) to determine the porosity of specimens, K=
ρ × 100%, ρ0
(2)
where K is the relative density, ρ is measured density, and ρ0 is theoretical density. X-ray diffraction (XRD: D8-ADVANCE, Bruker, MA, USA) was used to analyze the phase as the content of TiC increased. The wear amount of the specimen was measured by a ball-on-a-disk-type wear tester (High temperature wear tester, R&BCo. Ltd., Daejeon, Korea); the microstructure and indentation of the wear specimen were measured using scanning electron microscopy (SEM, S-4800, HITACHI, Chiyoda, Japan) and energy dispersive X-ray spectroscopy (EDS: EDAX, Bruker, MA, USA); hardness was measured using a Vickers hardness tester (VMT-X7, Matsuzawa, Akita, Japan); and bending strength was measured using the indentation fracture method at a load of 5N. Test specimens were prepared in 4mm × 8mm × 24 mm according to the KS D ISO 3325 standard [13] using a discharge wire.
Materials 2018, 11, 1133
3 of 10
They were then measured three times, and the bending strength was expressed using the average, maximum, and minimum range. The mixture design was processed in Minitab 17 (Minitab Inc., State College, PA, USA) using Materials 2018, 11, x FOR PEER REVIEW 3 of 10 the measured bending hardness, and wear loss. The vertex design represents Materials 2018, 11, x strength, FOR PEER REVIEW 3 ofthe 10 mixture wire.the They were then measured times,toand bending strength was expressed using the 1 shows design when composition ratio isthree limited thethe maximum and minimum, and Figure wire. They were then times, and the bending strength was expressed using the average, andmeasured minimum three a composite rate maximum, schematic diagram ofrange. the Ni-Ti-Al/TiC composite vertex design at ratios of 80:20, average, maximum, and minimum range. The mixture design was processed in Minitab 17 (Minitab Inc., State College, PA, USA) using 60:40 wt %the(angle point), andstrength, 70:30 wt % (middle point). Asvertex the utilizes deviations and The mixture design was processed inand Minitab 17 (Minitab Inc.,design State College, PA,two USA) using measured bending hardness, wear loss. The design represents the mixture the measured bending strength, hardness, and wear loss. The vertex design represents the mixture variances,design it waswhen performed twiceratio for iseach condition. The middle pointand was added to confirm the the composition limited to the maximum and minimum, Figure 1 shows a design when composition ratio is to the maximum minimum, Figure 1 shows composite rate schematic diagram ofproceeded thelimited Ni-Ti-Al/TiC composite vertex design atand ratios of 80:20, 60:40a between tendency between thethe two points and six times in and total. The degree of similarity composite rate schematic Ni-Ti-Al/TiC vertex utilizes design attwo ratios of 80:20, 60:40 % (angle point), and diagram 70:30 wtof%the (middle point).composite As the design deviations and the modelwt and data were analyzed using the measured values of hardness, bending wt %actual (angle point), and 70:30 (middle point). As middle the design two to deviations and strength, variances, it was performed twicewtfor%each condition. The pointutilizes was added confirm the and wear loss. Thebetween maximum ) was selected by the minimum value (Lconfirm and target value variances, it was performed for each condition. Theinmiddle point was of added to the Mtwice i ) between tendency the two(d points and proceeded six setting times total. The degree similarity tendency between thedata two points and proceeded times (d in m total. The degree of by similarity between (Ti ) of hardness and bending strength, and the minimum ) was setting the maximum the model and actual were analyzed using thesix measured values ofselected hardness, bending strength, the wear modelloss. andThe actual data were analyzed usingby thesetting measured values of hardness, maximum M ) wasThe selected the minimum (Li ) bending and target value value (Hi ),and and target value of wear(dloss. composite desirability isvalue expressed as astrength, combination of and wear loss. The maximum (d M ) was selected by setting the minimum value (L ) and value i (Ti ) of hardness and bending strength, and the minimum (dm) was selected by setting thetarget maximum the maximum d hardness or minimum d of individual desirability desirability function weight (ri ) was (Ti ) of and bending and thecomposite minimum(d). (dm)The was selected by setting maximum value (Hi ), and target value ofstrength, wear loss. The desirability is expressed as athe combination calculated of for individual desirability (d) and composite desirability when emphasizing the(riimportance value (Hi ), and target value of wear loss. The composite is expressed as a combination the maximum d or minimum d of individual desirabilitydesirability (d). The desirability function weight ) of the maximum d or minimum d of individual desirability (d). The desirability function weight (ri ) 0.1 and of each expected response value (yi ),desirability and the function is shown in Figure 2. Aemphasizing range between was calculated for individual (d) and composite desirability when the was calculated for expected desirability (d) desirability emphasizing the importance of each valuethe (yi ),and andcomposite the function shownwhen in the Figure 2. A value, range 10 is possible; if the value isindividual larger response than 1 then reaction value isiscloser to target whereas importance of each value (yi ), and the1 function shownvalue in Figure 2. Atorange between 0.1 and 10 isexpected possible;response if the value is larger than then the is reaction is closer the if it is lower than 1 then the optimum condition is found (even if the reaction value does not move between 0.1 whereas and 10 isifpossible; if than the value larger than 1condition then the reaction closer to the target value, it is lower 1 thenisthe optimum is found value (even is if the reaction close to the target value). target value, if it to is the lower thanvalue). 1 then the optimum condition is found (even if the reaction value does notwhereas move close target value does not move close to the target value).
Figure 1. Schematic diagram of Ni-Ti-Al/TiC composite ratios in mixture design using Minitab 17.
Figure 1. Schematic diagram of Ni-Ti-Al/TiC ratios in mixture design using 17. Minitab 17. Figure 1. Schematic diagram of Ni-Ti-Al/TiCcomposite composite ratios in mixture design using Minitab
(a) (a)
(b) (b)
Figure 2. Principle schematic diagram of applying weight of desirability function in mixture design. Figure 2. Principle of applying weight of desirability function in mixture design. Maximize diagram dM. (a) Minimize dm; (b) schematic Principle schematic diagram dM. of applying weight of desirability function in mixture (a) Minimize dm; (b) Maximize
Figure 2. (a) Minimize dm ; (b) Maximize dM . 3. Results and Discussion
design.
3. Results and Discussion Optimization of TiC Contents through the Mixture Design 3. Results3.1. and Discussion
3.1. Optimization of TiC Contents through the Mixture Design
3.1. Optimization of TiC Contents through the Mixture Design The reaction optimization tool can identify a single response or a combination of input variables and provide optimization of individual desirability and composite desirability. Individual desirability (d) is calculated in the range from 0 to 1 (where 1 is ideal and maximum (dM ) and minimum (dm )
Materials 2018, 11, x FOR PEER REVIEW Materials 2018, 11, 1133
4 of 10
4 of 10
The reaction optimization tool can identify a single response or a combination of input variables and provide optimization of individual desirability and composite desirability. Individual values are calculated based on formula (3). d is the distance d between maximum value (Hi ), minimum desirability (d) is calculated in the range from 0 to 1 (where 1 is ideal and maximum (dM) and value (Li ), the target value (Ti ) and the expected response value (yi ). The composite desirability (D) minimum (dm) values are calculated based on formula (3). d is the distance d between maximum is calculated in the range from 0 to 1 using Equation (4), by summing each response satisfaction, d, value (Hi ), minimum value (Li ), the target value (Ti ) and the expected response value (yi ). The shown in Equation (3), (D) is calculated in the range from 0 to 1 using Equation (4), by summing each composite desirability response satisfaction, d, shown in Equation (3), (yi −Li ) ri (Hi −yi ) ri r , minimize dm = ri maximize dM = , (3) ) i (yL (Hi -y (T − (H i -L i ) i −Ti ) i )i (3) , minimize dm = , maximize dM = i (Ti -Li ) (Hi -Ti ) 1/W r1 r2 composite desirability D = (d 1 ×d 2 × . . . × dn ) , (4) r r2 1/W (4) composite desirability D=(d 1 ×d 2 ×…×dn ) , where ri is the weight of the desirability function of the ith response; and W is Σri . where ri is the weight of the desirability function of the ith response; and W is Σri . Figure 3 shows the optimization of the composition using the reaction optimization tool. Figure 3 shows the optimization of the composition using the reaction optimization tool. This This experiment was conducted by choosing the same weight as 1 to determine the characteristics of experiment was conducted by choosing the same weight as 1 to determine the characteristics of mechanical properties, but not with respect to their commercialization. The optimum composition was mechanical properties, but not with respect to their commercialization. The optimum composition selected as 0.5873 (Ni-Ti-Al: 67.84 wt %, TiC: 32.16 wt %). However, individual satisfaction with respect was selected as 0.5873 (Ni-Ti-Al: 67.84 wt %, TiC: 32.16 wt %). However, individual satisfaction with to bending strength was low because of the large difference between the target and minimum values. respect to bending strength was low because of the large difference between the target and minimum Nevertheless, this composition was selected the slight individual satisfaction values. Nevertheless, this composition wasbecause selectedofbecause of increase the slightinincrease in individual with respect towith wearrespect loss and hardness compared to compared the increase in individual with respect satisfaction to wear loss and hardness to the increase in satisfaction individual satisfaction to bending strength. This experiment was used to confirm the feasibility of characterization and with respect to bending strength. This experiment was used to confirm the feasibility of optimization according to the composition of TiC, and it is acknowledged that the optimal composition characterization and optimization according to the composition of TiC, and it is acknowledged that ratio varycomposition depending on themay weight. In Figure 3b, weight of the desirability themay optimal ratio vary depending on the the bending-strength weight. In Figure 3b, the bending-strength function as 5. function is selected as 5. weightisofselected the desirability
Figure 3. Response optimizer for mixture design using Minitab 17. (a) All of response value weight Figure 3. Response optimizer for mixture design using Minitab 17. (a) All of response value weight of of desirability is 1; (b) Bending strength weigh of desirability is 5. desirability is 1; (b) Bending strength weigh of desirability is 5.
3.2. Effect of TiC Contents on Density and XRD Pattern Microstructure of Ni-Ti-Al/TiC Composites 3.2. Effect of TiC Contents on Density and XRD Pattern Microstructure of Ni-Ti-Al/TiC Composites Table 2 shows the theoretical, measured, and relative densities of the Ni-Ti-Al/TiC composites. 2 shows the theoretical, measured,and andmeasured relative densities of thedecreased Ni-Ti-Al/TiC AsTable the TiC content increased, the theoretical density values with composites. respect to As the thedecrease TiC content increased, the theoretical and measured density values decreased withsintering respect to in the composition ratio of Ni, which has a relatively high density. In addition, the decrease in the composition ratio of Ni, which has a relatively high density. In addition, sintering under the same sintering conditions shows that the relative density decreased under the condition
Materials 2018, 11, 1133 Materials 2018, 11, x FOR PEER REVIEW
5 of 10 5 of 10
under sintering conditions shows that the penetration relative density decreased under the condition of of 40 wtthe % same TiC. This is attributed to an insufficient of the low contact angle of Ni-Ti-Al 40 wt % TiC. This is attributed to an insufficient penetration of the low contact angle of Ni-Ti-Al between the particles of TiC, and the formation of pores during sintering due to the increase in TiC. between the particles of TiC, and the formation of pores during sintering due to the increase in TiC. Table 2. Density of Ni-Ti-Al/TiC composition. Table 2. Density of Ni-Ti-Al/TiC composition. TheoreticalDensity Density Theoretical 3) (g/cm 3 (g/cm ) Ni-Ti-Al/20 % TiC 5.59 Ni-Ti-Al/20 wt %wt TiC 5.59 Ni-Ti-Al/30 wt % TiC 5.50 Ni-Ti-Al/30 wt % TiC 5.50 Ni-Ti-Al/40 wt % TiC 5.41 Ni-Ti-Al/40 wt % TiC 5.41 Ni-Ti-Al/32.16 wt % TiC 5.48 Ni-Ti-Al/32.16 wt % TiC 5.48 Sample Sample
Measured Density Measured Density (g/cm3 ) 3 (g/cm ) 5.52 5.52 5.41 5.41 5.25 5.25 5.37 5.37
Relative Density Relative Density (g/cm3 ) 3 (g/cm ) 98.8% 98.8% 98.4% 98.4% 97.1% 97.1% 98.1% 98.1%
Figure Figure44shows showsthe thephase phasecomposition compositionof ofthe themixes mixesand andsintered sinteredcomposites. composites.The Themain mainphases phases found Ni,Ni, Ti,Ti, Al,Al, andand TiC,TiC, andand phases found in theinsintered composites are NiTi, foundininthe themixes mixesare are phases found the sintered composites areTiNiTi, 2 Ni, TiC, NiTiC, Ti, TiAl, Ti AlC complex phases and Ti, Ni, Al phases. As the content of TiC increased under Ti2Ni, Ni 3 Ti, TiAl, Ti 2 AlC complex phases and Ti, Ni, Al phases. As the content of TiC increased 3 2 the same condition, the peak TiCof increased in thein range of 20 of wt20 %wt to % 40to wt40%wt but under thesintering same sintering condition, theof peak TiC increased the range % the but Ti AlC peak decreased at 40 wt %. It is assumed that the TiC powder was incompletely sintered at the the Ti 2 AlC peak decreased at 40 wt %. It is assumed that the TiC powder was incompletely sintered 2 interface of Ni-Ti-Al and TiC in TiC theseinreactions [12]. XRD that atthat TiC at peak of 20 wt at the interface of Ni-Ti-Al and these reactions [12].showed XRD showed TiCvalues peak values of % 20 and 30and wt 30 %,wt TiC%,was to Ti2to AlC. In addition, withwith increased amounts of TiC, values of wt % TiCsynthesized was synthesized Ti2AlC. In addition, increased amounts of TiC, values Ni Ti 3and NiTi decreased andand the the Ni peak roserose duedue to the decreased Ni reaction. of3Ni Ti and NiTi decreased Ni peak to the decreased Ni reaction.
Figure4.4.XRD XRDanalyses analysesof ofNi-Ti-Al/TiC Ni-Ti-Al/TiC composition composition and and Ni-Ti-Al Ni-Ti-Al alloy. alloy. Figure
Figure55shows showsthe themicrostructure microstructureofof the fabricated Ni-Ti-Al/TiC composites with contents Figure the fabricated Ni-Ti-Al/TiC composites with TiCTiC contents of of 20, 30, 32.16, and 40 wt %. The TiC particle was uniformly distributed in the Ni-Ti-Al alloy matrix 20, 30, 32.16, and 40 wt %. The TiC particle was uniformly distributed in the Ni-Ti-Al alloy matrix at at TiC contents of and 20 and 30 wt number of fine-sized (3–5 μm) particles increased abruptly TiC contents of 20 30 wt %. %. TheThe number of fine-sized (3–5 µm) TiCTiC particles increased abruptly at at 32.16 wt % and 40 wt %. However, TiC and Ni-Ti-Al were not uniformly distributed at 40 wt % 32.16 wt % and 40 wt %. However, TiC and Ni-Ti-Al were not uniformly distributed at 40 wt % and and were found to be united. Table 2 and Figure 5 show that Ni-Ti-Al did not penetrate sufficiently were found to be united. Table 2 and Figure 5 show that Ni-Ti-Al did not penetrate sufficiently between between the TiCas particles as the content increased, in theofinterface TiC and Nithe TiC particles the content increased, resulting inresulting pores inin thepores interface TiC and of Ni-Ti-Al. Ti-Al. Figure 6 shows the microstructure and distribution of elements across the interface between the Figure shows the microstructure andby distribution elementsanalyses across the interface between the TiC and the 6Ni–Ti–C alloy, as determined EDS. EDS of mapping revealed a distribution TiC andfor thethe Ni–Ti–C alloy, as determined bydistributed EDS. EDSasmapping revealed a distribution gradient elemental composition: Ti was a whole,analyses and Ni, Al, and C were partially gradient for the elemental composition: Ti was distributed as a whole, and Ni, Al, were concentrated. The distributions and phases of TiC and Ni-Ti-Al alloys were confirmed andand are C shown partially concentrated. The distributions and phases of TiC and Ni-Ti-Al alloys were confirmed in Figures 4 and 6. The formation of Ti2AlC was observed using the compositional distribution at and the are shownbonding in Figures 4 and The formation of Ti2AlC was an observed using thelack compositional interfacial between the6.Ni-Ti-Al and TiC. Results showed almost complete of Ni in the distribution at the interfacial bonding between the Ni-Ti-Al and TiC. Results showed an almost complete lack of Ni in the interface between Ni-Ti-Al and TiC but a region where Al and C were
Materials 2018, 11, 1133
6 of 10
Materials 2018, 11, x FOR PEER REVIEW
6 of 10
interface between Ni-Ti-Al and TiC but a region where Al and C were common, which is considered to common, which considered be ainterval. Ti2AlC layer with a 0.5 to 1 μm interval. Figure 7 shows a line be a Ti2AlC layeriswith a 0.5 to to 1 µm Figure 7 shows a line scan analysis using EDS. Due to scannature analysis using EDS.REVIEW Due to theequipment, nature of high-energy sintering equipment, SPS, the components the of xhigh-energy sintering SPS, the components are seen to be diffused and were Materials 2018, 11, FOR PEER 6 of 10 are seen toas beadiffused anditwere measured a whole, it was possible to obtain high peaks at key measured whole, but was possible to as obtain highbut peaks at key locations. The decrease in the Ni common, which is considered to a Ti2AlC layer with a 0.5ofthe toNi-Ti-Al 1decrease μm interval. Figure 7Inshows a line locations. The decrease in the Nibe peak in the region and TiCAl was larger than the peak in the interface region of Ni-Ti-Al and TiCinterface was larger than in the peak. addition, decrease in using the Al peak. In addition, gray section confirmed to a Ti2AlC of scan analysis EDS. Due to the nature of high-energy sintering SPS,layer the components the gray section was confirmed to be athe Ti2AlC layer ofwas 0.5 µm, due toequipment, thebe distribution peak of0.5 C. μm, to to thebedistribution peak of C. aredue seen diffused and were measured as a whole, but it was possible to obtain high peaks at key 3Ni interface + Ti → Ni (5)the 3 Ti, of Ni-Ti-Al and TiC was larger than locations. The decrease in the Ni peak in the region
decrease in the Al peak. In addition, the gray section was confirmed to be a Ti2AlC layer of 0.5 μm, 3Ti + 2Al + 2Ni → TiAl, NiAl, Ti2 Ni, (6) due to the distribution peak of C.
Figure 5. Microstructure of Ni-Ti-Al/TiC composites by SPS BSE of: (a) TiC content 20 wt %; (b) TiC content 30 wt %; (c) TiC content 32.16 wt %; (d) TiC content 40 wt %.
3Ni + Ti → Ni Ti, .
(5)
Figure 5. 5.Microstructure SPS BSE BSEof: of:(a) (a)TiC TiCcontent content2020wtwt TiC Figure MicrostructureofofNi-Ti-Al/TiC Ni-Ti-Al/TiCcomposites composites by by SPS %;%; (b)(b) TiC (6) 3Ti + 2Al + 2Ni → TiAl, NiAl, Ti Ni, content 30 wt %; (c) TiC content 32.16 wt %; (d) TiC content 40 wt %. content 30 wt %; (c) TiC content 32.16 wt %; (d) TiC content 40 wt %.
3Ni + Ti → Ni Ti, .
(5)
3Ti + 2Al + 2Ni → TiAl, NiAl, Ti Ni,
(6)
Ti2AlC
Ti2AlC
Figure 6. SEM images and EDS elemental mapping analysis analysis of of Ni-Ti-Al/TiC Ni-Ti-Al/TiC composites.
Figure 6. SEM images and EDS elemental mapping analysis of Ni-Ti-Al/TiC composites.
Materials 2018, 11, 1133 Materials 2018, 11, x FOR PEER REVIEW
7 of 10 7 of 10
Figure 7. Microstructure and EDS analysis of interface between TiC and Ni-Ti-Al alloy.
3.3. Mechanical Properties of Ni-Ti-Al/TiC Composites Figure 8a shows a graph of changes in hardness with increases in the TiC composition. Hardness measured using a Vickers hardness meter was 8.3 GPa at 20 wt % TiC, but it increased to 9.75 at 30 wt %, and a further slight increase was detected at 40 wt % (from 9.75 GPa to 9.98 GPa). Figures 2 and 3 show that the TiC distribution was higher on the surface, and higher hardness was maintained with a content of 40 wt % due to the higher distribution of TiC on the surface; however the Ni-Ti-Al alloy was not infiltrated into the TiC particle and the surface was therefore easily broken due to the occurrence of the pores and an inactive interface. Figure 8b shows the bending strength according to the composition ratio, and it is evident that 7. Microstructure and EDS analysis of increasing interface between TiC andHowever, Ni-Ti-Al alloy. the value ofFigure the strength increases with an TiC content. the strength at Figure 7. bending Microstructure and EDS analysis of interface between TiC and Ni-Ti-Al alloy. TiC 20 wt % is lower than that of the conventional Ni-Ti-Al alloy. The bending strength was increased 3.3. Mechanical Properties of Ni-Ti-Al/TiC Composites in relation to the formation of Ti2AlC, and the formation of the NiTi phase was inhibited with an 3.3. Mechanical Properties of Ni-Ti-Al/TiC Composites increase in the number of TiC particles. This reason presumed strength of the base metal Figure 8a shows a graph of changes in hardnesswas with increasesbending in the TiC composition. Hardness and 30 wt %. The interfacial bonding energy increased for the TiC and Ni-Ti-Al alloy during Figure 8a shows graph hardness of changes in hardness with in the composition. measured using a aVickers meter was 8.3 GPa at increases 20 wt % TiC, but TiC it increased to 9.75 Hardness atthe 30 Ti 2 AlC phase. Figure 2 shows that when the content of TiC increased, formation of the NiTi phase wt %,using and a further slight increase was detected 40 wt % (from 9.75 GPa toincreased 9.98 GPa). to Figures 2 and measured a Vickers hardness meter was 8.3 at GPa at 20 wt % TiC, but it 9.75 at 30 wt %, inhibited, Ti 2AlC was produced. However, the bending strength at 20 wt % maintained and the bending show that theand TiC distribution higher on40 thewt surface, and 9.75 higher hardness was with and a3was further slight increase was was detected at % (from GPa to 9.98 GPa). Figures 2 and 3 strength of the base metal overlapped in the maximum superficial value however range, which suggestsalloy that a content of 40 wt % due to the higher distribution of TiC on the surface; the Ni-Ti-Al show that the TiC distribution was higher on the surface, and higher hardness was maintained with a the formation of NiTi suppressed but thethe formation Ti2therefore AlC was not smooth. was infiltrated intowas TiC particle and surface of was easily brokenThe duebending to the content ofnot 40 wt % due to thethe higher distribution of TiC on the surface; however the Ni-Ti-Al alloy was strength increased with and an increase in the TiC content: the highest bending strength was 311 MPa at occurrence of the pores an inactive interface. not infiltrated into thecomposite TiC particle and the surface was therefore easily due to the the optimization ratio of 32.16 wt %. However, thebroken hardness is occurrence high,that the of Figure 8b shows the bending strength according to thealthough composition ratio, andvalue it is evident the pores and an inactive interface. bending decreased due toincreases cracks relating internal pores [14]. However, the strength at the valuestrength of the bending strength with antoincreasing TiC content. TiC 20 wt % is lower than that of the conventional Ni-Ti-Al alloy. The bending strength was increased in relation to the formation of Ti2AlC, and the formation of the NiTi phase was inhibited with an increase in the number of TiC particles. This reason was presumed bending strength of the base metal and 30 wt %. The interfacial bonding energy increased for the TiC and Ni-Ti-Al alloy during the Ti2AlC phase. Figure 2 shows that when the content of TiC increased, formation of the NiTi phase was inhibited, and Ti2AlC was produced. However, the bending strength at 20 wt % and the bending strength of the base metal overlapped in the maximum superficial value range, which suggests that the formation of NiTi was suppressed but the formation of Ti2AlC was not smooth. The bending strength increased with an increase in the TiC content: the highest bending strength was 311 MPa at the optimization composite ratio of 32.16 wt %. However, although the hardness value is high, the bending strength decreased due to cracks relating to internal pores [14]. Figure 8. Effect of TiC contents on: (a) macro hardness and (b) bending stress. Figure 8. Effect of TiC contents on: (a) macro hardness and (b) bending stress.
Figure 8b shows the bending strength according to the composition ratio, and it is evident that the value of the bending strength increases with an increasing TiC content. However, the strength at TiC 20 wt % is lower than that of the conventional Ni-Ti-Al alloy. The bending strength was increased in relation to the formation of Ti2 AlC, and the formation of the NiTi phase was inhibited with an increase in the number of TiC particles. This reason was presumed bending strength of the base metal and 30 wt %. The interfacial bonding energy increased for the TiC and Ni-Ti-Al alloy during the Ti2 AlC phase. Figure 2 shows that when the content of TiC increased, formation of the NiTi phase was inhibited, and Ti2 AlC was produced. However, the bending strength at 20 wt % and the bending Figure 8. Effect of TiC contents on: (a) macro hardness and (b) bending stress. strength of the base metal overlapped in the maximum superficial value range, which suggests that the formation of NiTi was suppressed but the formation of Ti2 AlC was not smooth. The bending strength increased with an increase in the TiC content: the highest bending strength was 311 MPa at the optimization composite ratio of 32.16 wt %. However, although the hardness value is high, the bending strength decreased due to cracks relating to internal pores [14].
Materials 2018, 11, 1133
8 of 10
Materials 2018, 11, x FOR PEER REVIEW
8 of 10
Materials 2018, 11, x FORthe PEER REVIEWof wear at each TiC composition ratio according to a change8 in of load 10 Figure 9 shows amount Figure 9 shows theabrasion amount of wear at amount each TiCof composition ratio according to a change in the ball-on-disk type test: the wear increased with an increase in in theload load. theFigure ball-on-disk abrasion test: amount of wear with an increase in the The showstype thewas amount of wear at each TiC composition ratio according change in load Theinamount of9 abrasion lowest atthe a TiC content of 30increased wt % and highest at to 40awt %. load. There was amount of abrasion was lowest test: at a the TiCamount contentofofwear 30 wt % and highest at 40 wt %. There was a in the ball-on-disk type abrasion increased with an increase in the load. The a decrease in the abrasion amount at 30 wt % compared to 20 wt % due to the increase in hardness decreaseof in abrasion the abrasion wt %content compared 20 wt % due to theat increase in hardness and amount wasamount lowest at 30 a TiC of 30towt % and highest 40 wt %. There was a and bending strength. Although the TiC specimen at 40 wt % had a high density due to use of the bending strength. Although the at TiC at 40 wt a high density due toinuse of the high decrease in the abrasion amount 30specimen wt % compared to% 20had wt % due to the increase hardness and high plasma density sintering method, the Ni-Ti-Al base material could not sufficiently bond with plasma density sintering method, the Ni-Ti-Al base material could not sufficiently bond with the TiC. bending strength. Although the TiC specimen at 40 wt % had a high density due to use of the high the TiC. Therefore, the abrasion rate also increased rapidly when the TiC particles dropped out after Therefore, the abrasion also increased rapidly thecould TiC particles droppedbond out after plasma density sinteringrate method, the Ni-Ti-Al basewhen material not sufficiently with the load TiC. theincreased load increased [14,15]. In addition, the optimum condition wtmore % caused more abrasion In addition, theincreased optimum condition of 32.16 wtof %32.16 caused 30 Therefore,[14,15]. the abrasion rate also rapidly when the TiC particles droppedabrasion out afterthan the at load than wtthe %,difference but the difference was only slight. wtat %,30 but was only slight. increased [14,15]. In addition, the optimum condition of 32.16 wt % caused more abrasion than at 30 wt %, but the difference was only slight.
Figure9.9.Effect EffectofofTiC TiCcontent content on on wear wear loss loss according Figure accordingto toload loadvarious. various. Figure 9. Effect of TiC content on wear loss according to load various.
Figure 10 shows photographs of the surfaces of wear test specimens. The cracks and traces of Figure 10 shows photographs of the surfaces of wear test specimens. The cracks and traces of the the wear tracks are more highly evident 20 wt % wtspecimens. % than at 30 %, and craters Figure 10 shows photographs of the at surfaces of and wear40test Thewtcracks and tracesare of wear tracks are more highly evident at 20 the wt unsintered % and 40 wt % than at were 30 wt %, and craters are evident evident 40 wt %. was confirmed that TiC each other the wearattracks areItmore highly evident at 20 wt % and 40particles wt % than atseparated 30 wt %, from and craters are at 40 %.secondary It was confirmed that the unsintered TiC separated from 10e each other and andwt that occurred. addition, theparticles result ofwere EDSwere shown in Figure evidences evident at 40 wt %. Itwear was had confirmed thatIn the unsintered TiC particles separated from each other that secondary wear had occurred. In addition, the result of EDS shown in Figure 10e evidences the reduction in areas of abrasion at 30 wt %, which relates to the high TiC composition [15,16]. and that secondary wear had occurred. In addition, the result of EDS shown in Figure 10e evidencesthe reduction in areas of abrasion at 30at wt30%, relates to the high TiCTiC composition [15,16]. the reduction in areas of abrasion wtwhich %, which relates to the high composition [15,16].
Figure 10. Cont.
Materials 2018, 11, 1133 Materials 2018, 11, x FOR PEER REVIEW
9 of 10 9 of 10
Figure 10. Abrasion surface of Ni-Ti-Al/TiC composites by SPS SEM image of (a) TiC content of 20 wt Figure 10. Abrasion surface of Ni-Ti-Al/TiC composites by SPS SEM image of (a) TiC content of %; (b) TiC content of 30 wt %; (c) TiC content of 32.16 wt %; (d) TiC content of 40 wt %; and EDS 20 wt %; (b) TiC content of 30 wt %; (c) TiC content of 32.16 wt %; (d) TiC content of 40 wt %; and EDS analysis showing (e) TiC content of 30 wt %. analysis showing (e) TiC content of 30 wt %.
4. Conclusions 4. Conclusions TiC was added to an Ni-Ti-Al alloy, which is a high-temperature structural material, and TiC was bending added tostrength, an Ni-Ti-Al is a high-temperature structural material, and hardness, hardness, andalloy, wearwhich loss were measured at room temperature. The optimum bending strength, and wear loss measured at roommethod. temperature. The optimum condition condition was determined usingwere the mixture synthesis The optimum composition ratio was is determined using thea mixture synthesis optimum ratio considered be a considered to be factor that can bemethod. used toThe improve the composition durability life of isthe product. to The factor that can be usedthe to improve the durability life of the product. using the highest composition using highest composite desirability was selectedThe for composition all three compositions with composite desirability was selected for thus all three compositions with high individual desirabilities, which high individual desirabilities, which suggests the possibility of optimization. thus suggests the possibility of optimization. 1. The Ti2AlC phase was increased with the addition of TiC, but the Ti2AlC phase was not formed sufficiently between interfaces duethe to the failureofofTiC, TiC but particles penetrate smoothly at 40 1. The Ti2 AlC phase wasthe increased with addition the Tito 2 AlC phase was not formed wt %. High densification was achieved using the spark plasma sintering method. smoothly However, at sufficiently between the interfaces due to the failure of TiC particles to penetrate density was reduced with an increase in the TiC content, and pores were generated at interfaces 40 wt %. High densification was achieved using the spark plasma sintering method. However, between TiC and Ni-Ti-Al. density was reduced with an increase in the TiC content, and pores were generated at interfaces 2. The hardness value increased with an increase in the TiC content, and the highest hardness value between TiC and Ni-Ti-Al. was measured at 40 wt %. In addition, TiC was saturated on the surface at 40 wt % and an The hardness value increased with an increase in the TiC content, and the highest hardness value 2. increase range of hardness was decreased from 9.75 GPa to 9.98 GPa. at 40 wtwas %. increased In addition, was saturated the surface 40 wt %ofand 3. was Themeasured bending strength dueTiC to the formation of on Ti2AlC, and theat formation thean increase range of hardness was decreased from 9.75 GPa to 9.98 GPa. NiTi phase was inhibited with an increase in the TiC particles. The interfacing bonding energy 3. The bending strength due to the formation of Tiphase. andTithe formation of the 2 AlC,The increased between thewas TiC increased and Ni-Ti-Al alloy during the Ti2AlC 2AlC peak at 32.16 NiTi phase was inhibited with an increase in the TiC particles. The interfacing bonding energy wt % was superior to that of the other content materials and the bending strength was superior increased between the TiC and Ni-Ti-Al alloy during the Ti2 AlC phase. The Ti2 AlC peak at at 311 MPa. was superior to that of theon other content materials and the bending strength was 4. 32.16 Thewt TiC%content has a significant effect the wear resistance of the composites. At a TiC content of 30 wtat%, the weight loss of the composites reached a minimum value of 2.2 mg. Secondary superior 311 MPa. wear withathe TiC particle byon spalling at TiC 40 wt %. The TiCoccurred content has significant effect the wear resistance of the composites. At a TiC content 4.
of 30 wt %, the weight loss of the composites reached a minimum value of 2.2 mg. Secondary
Author Contributions: D.-J.L. did the experiments, data analysis and wrote part of paper, J.-H.P. did data wear occurred with the TiC particle by spalling at TiC 40 wt %. analysis and proofread the paper; M.-C.K. provided the original ideas.
Funding: This work was supported by a 2-Year Research Grant (201705660002) of Pusan National University. Author Contributions: D.-J.L. did the experiments, data analysis and wrote part of paper, J.-H.P. did data analysis TheM.-C.K. first andprovided the second contributed equally to this work. andAcknowledgments: proofread the paper; theauthors original ideas.
Funding: This wasThe supported by a 2-Year Research Grant (201705660002) of Pusan National University. Conflicts of work Interest: authors declare no conflict of interest. Acknowledgments: The first and the second authors contributed equally to this work.
References
Conflicts of Interest: The authors declare no conflict of interest. 1. Koizumi, Y.; Ro, Y.; Nakazawa, S.; Harada, H. NiTi-base intermetallic alloys strengthened by Al substitution. Mater. Sci. Eng. A 1997, 223, 36–41. References 2. Meng, L.; Li, Y.; Zhao, X.; Xu, J.; Xu, H. The mechanical properties of intermetallic Ni50−xTi50Alx alloys (x = 1. Koizumi, Y.;Intermetallics Ro, Y.; Nakazawa, S.;814–818. Harada, H. NiTi-base intermetallic alloys strengthened by Al substitution. 6, 7, 8, 9). 2007, 15, Mater. Sci. Eng. A 1997, 223, 36–41. [CrossRef] 3. Zhou, L.; Zheng, L.J.; Zhang, H. Effect of heating temperature on microstructure of directionally solidified 2. Meng, Zhao, X.; Xu, J.; Xu, 2017, H. The mechanical Ti-7Li, Al Y.; alloy. Mater. Sci. Forum 898, 552–560. properties of intermetallic Ni50−x Ti50 Alx alloys (x = Ni-43L.; 6, 7, 8, 9). Intermetallics 2007, 15, 814–818. [CrossRef]
Materials 2018, 11, 1133
3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
10 of 10
Zhou, L.; Zheng, L.J.; Zhang, H. Effect of heating temperature on microstructure of directionally solidified Ni-43 Ti-7 Al alloy. Mater. Sci. Forum 2017, 898, 552–560. [CrossRef] Song, X.; Li, Y.; Zhang, F. Microstructure and tensile properties of isothermally forged Ni–43 Ti–4 Al–2 Nb–2 Hf alloy. Rare Met. 2013, 32, 475–479. [CrossRef] Song, X.; Li, Y.; Zhang, F. Microstructure and mechanical properties of Nb- and Mo-modified NiTi–Al-based intermetallics processed by isothermal forging. Mater. Sci. Eng. A 2014, 594, 229–234. [CrossRef] Song, X.; Li, Y.; Zhang, F.; Li, S. NiTiAl intermetallic alloys strengthened by Mo replacement. Chin. J. Aeronaut. 2010, 23, 715–719. Li, Y.; Yu, K.; Song, X.; Zhang, F. Effect of Zr addition on microstructures and mechanical properties of Ni-46 Ti-4 Al alloy. Rare Met. 2011, 30, 522–526. [CrossRef] Xu, H.; Meng, L.; Xu, J.; Li, Y.; Zhao, X. Mechanical properties and oxidation characteristics of TiNiAl (Nb) intermetallics. Intermetallics 2007, 15, 778–782. [CrossRef] Xiaoyun, S.; Wenjun, Y.; Songxiao, H.; Yan, L. Oxidation behavior of NiTi-Al based alloy with Nb and Mo additions. IOP Conf. Ser. Mater. Sci. Eng. 2017, 250, 1–5. [CrossRef] Zheng, Y.; Zhou, Y.; Li, R.F.; Wang, J.Q.; Chen, L.L.; Li, S.B. Preparation and mechanical properties of TiC-Fe cermets and TiC-Fe/Fe bilayer composites. J. Mater. Eng. Perform. 2017, 26, 4933–4939. [CrossRef] Wang, Z.; Lin, T.; He, X.B.; Shao, H.P.; Tang, B.; Qu, X.H. Fabrication and properties of the TiC reinforced high-strength steel matrix composite. Int. J. Refract. Met. Hard Mater. 2016, 58, 14–21. [CrossRef] Liu, N.; Chen, M.H.; Xu, Y.D.; Zhou, J.; Shi, M. Wettability and bonding between Ni and Ti(C, N) with multiple carbide additions. J. Mater. Sci. Technol. 2005, 21, 53–59. Korean Standards Association. Sintered Materials, Excluding Hard Metals—Determination of Transverse Rupture Strength; KS D ISO 3325; Korean Standards Association: Seoul, Korea, 2011. Gonzalez, J.J.; Llorente, J.; Bram, M.; Belmonte, M.; Guillon, O. Novel Cr2 AlC MAX-phase/SiC fiber composites: Synthesis, processing and tribological response. J. Eur. Ceram. Soc. 2017, 37, 467–475. [CrossRef] Wang, Y.; Lei, K.; Ruan, Y.; Dong, W. Microstructure and wear resistance of c-BN/Ni–Cr–Ti composites prepared by spark plasma sintering. Int. J. Refract. Met. Hard Mater. 2016, 54, 98–103. [CrossRef] Bin, C.; Ye, F.T.; Long, H.E.; Hua, T.; Li, G. Tribological properties of TiC particles reinforced Ni-based alloy composite coatings. Trans. Nonferr. Met. Soc. China 2013, 23, 1681–1688. © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
