materials Article
Microstructure and Mechanical Properties of TiC0.7N0.3-HfC-WC-Ni-Mo Cermet Tool Materials Jiaojiao Gao 1,2 , Jinpeng Song 1,2, * and Ming Lv 1,2, * 1 2
*
School of Mechanical Engineering, Taiyuan University of Technology, Taiyuan 030024, China;
[email protected] Shanxi Key Laboratory of Precision Machining, The Shanxi Science and Technology Department, Taiyuan University of Technology, Taiyuan 030024, China Correspondence:
[email protected] (J.S.);
[email protected] (M.L.)
Received: 3 May 2018; Accepted: 5 June 2018; Published: 8 June 2018
Abstract: TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials were fabricated by hot pressing technology at 1450 ◦ C. The effects of WC (tungsten carbide) content on the microstructure and mechanical properties of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials were investigated. The results showed that the TiC0.7 N0.3 -HfC-WC-Ni-Mo cermets were mainly composed of TiC0.7 N0.3 , Ni, and (Ti, Hf, W, Mo)(C, N); there were three phases: a dark phase, a gray phase, and a light gray phase. The dark phase was the undissolved TiC0.7 N0.3 , the gray phase was the solid solution (Ti, Hf, W, Mo)(C, N) poor in Hf, W, and Mo, and the light gray phase was the solid solution (Ti, Hf, W, Mo)(C, N) rich in Hf, W, and Mo. The increase of WC content could promote the process of HfC to form a solid solution and the HfC formed a solid solution more easily with WC than with TiCN. The increase of the solid solution made the microstructure more uniform and the mechanical properties better. In addition, the Vickers hardness, flexural strength, and fracture toughness of the TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet increased with the increase of WC content. When the content of WC was 32 wt %, the cermet obtained the optimal comprehensive mechanical properties in this investigation. The toughening mechanism of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials included solid solution toughening, particle dispersion toughening, crack bridging, and crack deflection. Keywords: TiCN-HfC-WC cermet; hot-pressed sintering; microstructure; mechanical properties
1. Introduction TiCN-based cermet tool material has developed rapidly in recent years and exhibits excellent characteristics in high-speed cutting [1]. It has excellent properties such as good wear resistance, excellent high temperature hardness, a relatively low friction coefficient, and superior chemical stability [2,3]. Compared with the traditional WC-Co tool, the TiCN cermet tool has better thermal stability, high temperature oxidation resistance, high temperature hardness, and lower fracture toughness [4–6]. Recently, researchers have conducted a lot of research on how to improve the fracture toughness of TiCN cermet. Yin et al. [2] investigated the effect of the microwave sintering process and WC/Mo2 C ratio on the mechanical properties of TiCN-based cermet cutting tool material, and reported that the fracture toughness was 10.08 MPa·m1/2 and the hardness was 16.83 GPa. Verma et al. [5] investigated the effect of TaC addition on the mechanical properties of Ti(CN)-5 wt % WC-20 wt % Ni/Co cermets and reported that the fracture toughness was 9.51 MPa·m1/2 and the hardness was 17.01 GPa. Liu et al. [1] investigated the influence of Mo2 C and TaC additions on the mechanical properties of TiCN-based cermets, and pointed out that the fracture toughness was about 13.5 MPa·m1/2 , the transverse rupture strength was about 1690 MPa, and the hardness was about 91.4 HRA. Park et al. [7] investigated carbide/binder interfaces in Ti(CN)-(Ti, W)C/(Ti, Materials 2018, 11, 968; doi:10.3390/ma11060968
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W)(CN)-based cermets and the result showed that the fracture toughness was 12.2 MPa·m1/2 and the hardness was 14 GPa. Sun et al. [8] investigated the effect of short carbon fiber concentration on the mechanical properties of TiCN-based cermets and stated that the fracture toughness was 11.66 MPa·m1/2 , the bending strength was 643.3 MPa, and the hardness was 79.1 HRA. It can be noted that there has been a great breakthrough in improving the fracture toughness of TiCN-based cermet, but its hardness has not improved simultaneously. Its low hardness limits its extensive application in high-speed cutting. Therefore, it is necessary to improve the comprehensive mechanical properties of TiCN-based cermet. In many investigations, WC plays an important role in enhancing the microstructure and mechanical properties of TiCN-based cermet. Dong et al. [9] reported that the mechanical properties of nano Ti(C, N)-based cermet were improved with the increase of WC addition. Qu et al. [10] reported that the lattice constant of the Ti(C, N) hard phase increased with the increase of WC content. Wang et al. [11] reported that WC can enhance density, facilitate sintering, and decrease the particle growth rate of TiCN-based cermet, and that Mo is almost necessary for Ti(CN)-based cermets. However, there are few reports on the effect of WC on the microstructure and mechanical properties of TiCN-HfC cermet. Besides, Mun et al. [12] reported that the addition of HfC could improve the cutting performance of TiCN-based cermet tools and Song et al. [13] pointed out that HfC addition could inhibit grain growth in TiN-based and TiB2 -based ceramic tools. Based on our previous investigation [14], HfC plays a positive role in improving the microstructure and mechanical properties of TiCN-based cermet tools. In order to further improve the comprehensive mechanical properties of TiCN-HfC cermet, the effect of WC content on the microstructure and mechanical properties of TiCN-HfC-Ni-Mo cremet was investigated in this work. 2. Experimental Procedure The composition of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermets and the specifications of raw powders are showed in Tables 1 and 2. Table 1. Composition ratios of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermets (wt %). Specimen
TiC0.7 N0.3
HfC
WC
Ni
Mo
W8 W16 W24 W32
64 56 48 40
20 20 20 20
8 16 24 32
4 4 4 4
4 4 4 4
Table 2. Specifications of raw powders. Powders
Size
Purity
Manufacturer
TiC0.7 N0.3 HfC WC Ni Mo
1 µm 0.8 µm 0.1 µm 1 µm 1 µm
>99% >99% >99% >99% >99%
Shanghai ST-Nano Science and Technology Co., Ltd., Shanghai, China Shanghai Chaowei Nanomaterials Co., Ltd., Shanghai, China Shanghai Yunfu Nanotechnology Co., Ltd., Shanghai, China Shanghai Yunfu Nanotechnology Co., Ltd., Shanghai, China Shanghai Yunfu Nanotechnology Co., Ltd., Shanghai, China
The powders were mixed and milled for 48 h in a polyethylene jar with WC (tungsten carbide) balls and alcohol as mediums. Then the mixed slurry was dried in vacuum and sieved by a 200-mesh sieve. Then, the mixed powder was sealed and compacted into graphite mold at room. The compacted powders were sintered in a vacuum ((1.2−2.4) × 10−3 Pa) hot-press sintering furnace (ZT-40-20, Shanghai Chenhua Technology Co., Ltd., Shanghai, China). The sintering parameters were as follows: the sintering temperature was 1450 ◦ C, the holding time was 30 min, the heating rate was 50 ◦ C/min, and the sintering pressure was 30 MPa. The sintered samples were cut into testing specimens by
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the electrical discharge wire cutting method and the surfaces of the testing bars were polished Materials 2018, 11, x FOR PEER REVIEW 3 of 9 using diamond slurries. The dimensions of the specimen were 3 mm × 4 mm × 40 mm. specimens by the electrical discharge wire cutting method and the surfaces of the testing bars were Flexural strength was measured at a span of 30 mm and across a head speed of 0.5 mm/min by the polished using diamond slurries. The dimensions of the specimen were 3 mm × 4 mm × 40 mm. three-point bending test method on an electron universal tester (CREE-8003G, Dongguan City Kerry Flexural strength was measured at a span of 30 mm and across a head speed of 0.5 mm/min by Instrument Technology Co., Ltd., Dongguan, China) according to Chinese National Standards GB/T the three‐point bending test method on an electron universal tester (CREE‐8003G, Dongguan City 6569-2006/ISO 14704: 2000 [15]. Fracture toughness (KIC ) was measured via the direct indentation Kerry Instrument Technology Co., Ltd., Dongguan, China) according to Chinese National Standards method [16,17]. Vickers hardness was[15]. measured ontoughness the polished using a diamond pyramid GB/T 6569‐2006/ISO 14704: 2000 Fracture (KIC) surfaces was measured via the direct indenter (HVS-30, Shanghai Precision Instruments Co., measured Ltd., Shanghai, China) under a loadusing of 196a N for indentation method [16,17]. Vickers hardness was on the polished surfaces diamond Precision Instruments [18]. Co., The Ltd., Shanghai, China) 15 s by HV-120pyramid based onindenter Chinese(HVS‐30, NationalShanghai Standards GB/T 16534-2009 relative density of each under a load of 196 N for 15 s by HV‐120 based on Chinese National Standards GB/T 16534‐2009 [18]. specimen was measured by the Archimedes method with distilled water as the medium. The theoretical The relative density of each specimen was measured by the Archimedes method with distilled water density was calculated according to the rule of mixtures based on the following densities: 5.08, 12.7, as the medium. The theoretical density was calculated according to the rule of mixtures based on the 15.6, 8.90, and 10.20 g/cm3 for TiC0.7 N0.3 , HfC, WC, Ni, and Mo, respectively. At least 15 specimens following densities: 5.08, 12.7, 15.6, 8.90, and 10.20 g/cm3 for TiC0.7N0.3, HfC, WC, Ni, and Mo, were tested for each experimental condition. X-ray diffraction (XRD, EMPYREAN, PANalytical B.V., respectively. At least 15 specimens were tested for each experimental condition. X‐ray diffraction Almelo, The Netherlands) and energy dispersive spectrometry (EDS, ACT-350, Oxford Instruments, (XRD, EMPYREAN, PANalytical B.V., Almelo, The Netherlands) and energy dispersive spectrometry Oxford, UK) were used to analyze the compositions the used composite. A scanning electron microscope (EDS, ACT‐350, Oxford Instruments, Oxford, UK) of were to analyze the compositions of the and acomposite. A scanning electron microscope and a back‐scattered electron microscope (SEM, Supra‐ back-scattered electron microscope (SEM, Supra-55, Carl Zeiss AG, Oberkochen, Germany) were used55, Carl Zeiss AG, Oberkochen, Germany) were used to observe the polished surface and fractured to observe the polished surface and fractured surface morphologies. surface morphologies.
3. Results and Discussion 3. Results and Discussion
3.1. Effects of WC Content on the Microstructure of TiC0.7 N0.3 -HfC-WC-Ni-Mo Cermets 3.1. Effects of WC Content on the Microstructure of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo Cermets
Figure 1 exhibits the XRD patterns of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials. The main Figure 1 exhibits the XRD patterns of TiC 0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials. The main phases were TiC0.7 N0.3 , Ni and (Ti, Hf, W, Mo)(C, N). The solid solution (Ti, Hf, W, Mo)(C, N) had a phases were TiC 0.7N0.3, Ni and (Ti, Hf, W, Mo)(C, N). The solid solution (Ti, Hf, W, Mo)(C, N) had a similar lattice structure to that of TiC0.7 N0.3 and solid solutions similar to that of (Ti, W/Ta/Mo . . . ) similar lattice structure to that of TiC0.7N0.3 and solid solutions similar to that of (Ti, W/Ta/Mo…)(C, (C, N) were also found in other researches [1,5,11]. In the liquid-phase sintering stage, TiC0.7 N0.3 , WC, N) were also found in other researches [1,5,11]. In the liquid‐phase sintering stage, TiC0.7N0.3, WC, HfC, and Mo dissolved, and then precipitated as a complex solid solution, (Ti, Hf, W, Mo)(C, N). HfC, and Mo dissolved, and then precipitated as a complex solid solution, (Ti, Hf, W, Mo)(C, N). TiC
N0.3 Ni (Ti,Hf,W,Mo)(C,N)
0.7
Relative intensity
20
30
40
50
60
70
80
90
2 (deg.)
Figure 1. R‐ray diffraction (XRD) patterns of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials.
Figure 1. R-ray diffraction (XRD) patterns of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials.
Figure 2 shows the SEM micrographs of polished surfaces of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet
Figure 2 shows the SEM micrographs of polished surfaces of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials with different WC contents. There were three phases including a dark phase, a gray phase, and a light gray phase, as shown by the arrows in Figure 2. The EDS result of each phase is tool materials with different WC contents. There were three phases including a dark phase, a gray exhibited in Figure 3. Based on the results of the XRD and EDS, the dark phase was the remanent phase, and a light gray phase, as shown by the arrows in Figure 2. The EDS result of each phase is TiCN with abundant Ti and scanty W, Hf, and Mo, as shown in Figure 3a; the gray phase was the exhibited in Figure 3. Based on the results of the XRD and EDS, the dark phase was the remanent TiCN complex solid solution (Ti, Hf, W, Mo)(C, N) poor in W, Hf, Mo and rich in Ti, as shown in Figure 3b; with abundant Ti and scanty W, Hf, and Mo, as shown in Figure 3a; the gray phase was the complex and the light gray phase was the complex solid solution (Ti, Hf, W, Mo)(C, N) rich in W, Hf, Mo solid solution (Ti, Hf, W, Mo)(C, N) poor in W, Hf, Mo and rich in Ti, as shown in Figure 3b; and the light elements but poor in Ti, as shown in Figure 3c. Qu et al. [10] reported that WC and Mo dissolved and gray then reprecipitated as phase was the complex solid solution (Ti, Hf, W, Mo)(C,Mo)(C, N) in N) rich in W,the Ti(C, Hf, Mo N)‐WC‐Mo‐Ni elements but poor solid solutions (Ti, W)(C, N) and (Ti, in Ti,cermet, as shown in Figure 3c. Qu et al. [10] reported that WC and Mo dissolved and then reprecipitated respectively; Mun et al. [12] reported that the solid solution (Ti, Hf)C formed in the as solid solutions (Ti, W)(C, N) and (Ti, Mo)(C, N) in the Ti(C, N)-WC-Mo-Ni cermet, respectively; Mun et al. [12] reported that the solid solution (Ti, Hf)C formed in the dissolution-reprecipitation
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process in the TiC-HfC-Ni cermet; Kumar et al. [19] reported that (Ti, W/Nb/Ta/Hf)CN 4 of 9 formed Materials 2018, 11, x FOR PEER REVIEW and reprecipitated around the undissolved TiCN in the TiCN-based cermets; therefore, the solid dissolution‐reprecipitation in from the TiC‐HfC‐Ni cermet; Kumar et al. [19] reported that solution (Ti, Hf, W, Mo)(C, N)process resulted the dissolution-reprecipitation process. Zhou et (Ti, al. [20] W/Nb/Ta/Hf)CN formed and reprecipitated around the undissolved TiCN in the TiCN‐based reported that the solid solution (Mo, Ti)(C, N) can improve the interface bonding strength between the solid solution Hf, W, Mo)(C, from N) resulted Ti(C,cermets; N) and therefore, Ni. In Figure 2 with the WC(Ti, content increased 8 to 32 from wt %,the thedissolution‐ change in the reprecipitation process. Zhou et al. [20] reported that the solid solution (Mo, Ti)(C, N) can improve size of the dark phase was not obvious, which was in the range of 0.5–3 µm, but the number of the interface bonding strength between Ti(C, N) and Ni. In Figure 2 with the WC content increased the dark phase decreased gradually, which indicated that the higher content of WC promoted the from 8 to 32 wt %, the change in the size of the dark phase was not obvious, which was in the range dissolution-reprecipitation process. In addition, there were some flaws (marked by circles) in Figure 2 of 0.5–3 μm, but the number of the dark phase decreased gradually, which indicated that the higher and content of WC promoted the dissolution‐reprecipitation process. In addition, there were some flaws the flaw mostly presented in the light gray phase, which showed that the light gray phase was a weak phase. With the WC content increasing, the number of flaws decreased gradually. In particular, (marked by circles) in Figure 2 and the flaw mostly presented in the light gray phase, which showed when the WC content increased to 32 wt %, there were almost no flaws in Figure 2d, which indicated that the light gray phase was a weak phase. With the WC content increasing, the number of flaws thatdecreased gradually. In particular, when the WC content increased to 32 wt %, there were almost no the quality of the polished surface was improved. The shapes of the flaws showed that the flaws in Figure 2d, which indicated that the quality of the polished surface was improved. The shapes formation of flaws was mainly due to the pull-off of the grains during the grinding and polishing of the flaws showed that the formation of flaws was mainly due to the pull‐off of the grains during process [13], which showed that the grain bonding strength was weak. So the improved quality of the the grinding and polishing process [13], which showed that the grain bonding strength was weak. So polished surface indicated that the grains bonding strength increased with the WC content increasing. the improved quality of the polished surface indicated that the grains bonding strength increased The main reason for this was that the wettability of Ni to WC was very good, far superior to the with the WC content increasing. The main reason for this was that the wettability of Ni to WC was wettability of Ni to TiCN and HfC. Therefore, with the WC content increasing, the number of flaws very good, far superior to the wettability of Ni to TiCN and HfC. Therefore, with the WC content decreased gradually. The improvement of the grain bonding strength can restrain crack propagation increasing, the number of flaws decreased gradually. The improvement of the grain bonding strength and then improve the fracture toughness of the cermet. Apart from the removed grains, some pores can restrain crack propagation and then improve the fracture toughness of the cermet. Apart from probably forming in the sintering process were parts of the flaws. the removed grains, some pores probably forming in the sintering process were parts of the flaws.
Figure 2. SEM micrographs of polished surfaces of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials
Figure 2. SEM micrographs of polished surfaces of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials 0.7N0.3‐HfC‐8 wt % WC (W8); (b) TiC 0.7N0.3‐HfC‐16 wt % WC (W16); with different WC contents: (a) TiC with(c) TiC different WC contents: (a) TiC N -HfC-8 wt % WC (W8); (b) TiC N 0.7 0.3 0.7 0.3 -HfC-16 wt % WC 0.7N0.3‐HfC‐24 wt % WC (W24); (d) TiC0.7N0.3‐HfC‐32 wt % WC (W32). (W16); (c) TiC0.7 N0.3 -HfC-24 wt % WC (W24); (d) TiC0.7 N0.3 -HfC-32 wt % WC (W32).
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(a)
(b)
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(c)
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Light gray phase
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Hf
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(a) N CTi
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(b)
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Hf
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Mo
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Hf Mo
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Hf Ni
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(c)
Gray phase Hf W Hf W
Light gray phase C
0
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Hf W
Ti
Mo
4
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W Hf W
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Hf
Ti Figure 3. 3. Energy Energy dispersive dispersive spectrometry spectrometry (EDS) (EDS) results ofof the the phases phases TiC ‐HfC‐WC‐Ni‐Mo Figure results inin TiC NN0.30.3-HfC-WC-Ni-Mo 0.70.7 Hf cermet tool materials: (a) EDS results of the dark phase; (b) EDS results of the gray phase; (c) EDS cermet tool materials: (a) EDS results of the dark phase; (b) EDS results of theTi gray phase; (c) EDS W Hf W Ti W N of Hf Hf W results of the light gray phase. results Hf the light gray phase. N Hf Mo Hf W Ti Ti W Ni Hf W CTi
NiHf
Mo
Hf
Ni
C
C
Mo
2 4 6 8 10 0 2 4 6 8 10 0 Figure 4 shows the fracture morphologies of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials Figure Figure 4 shows the fracture ofresults TiC0.7of Nthe cermet tool materials 3. Energy dispersive morphologies spectrometry (EDS) phases in TiC0.7N0.3‐HfC‐WC‐Ni‐Mo 0.3 -HfC-WC-Ni-Mo with different WC contents. The core‐rim structure (marked by squares) was obvious in these cermets. cermet tool materials: (a) EDS results of the dark phase; (b) EDS results of the gray phase; (c) EDS with different WC contents. The core-rim structure (marked by squares) was obvious in these cermets. During the sintering, HfC, WC, and Mo dissolved and then reprecipitated as the solid solution (Ti, results of the light gray phase. During the sintering, HfC, WC, and Mo dissolved and then reprecipitated as the solid solution (Ti, Hf, Hf, W, Mo)(C, N) to form the rim around the core—undissolved TiCN. When the WC content was 8 W, Mo)(C, N) to form the rim aroundmorphologies the core—undissolved TiCN. When the WCtool content was 8 and Figure 4 shows the fracture of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet materials and 16 wt %, there were some big size dark phases (marked by circles in Figure 4a,b) which made the 16 wt %,with different WC contents. The core‐rim structure (marked by squares) was obvious in these cermets. there were some big size dark phases (marked by circles in Figure 4a,b) which made the microstructure uneven. In contrast, the microstructure was fine and uniform in Figure 4c,d when the microstructure uneven. In contrast, the microstructure was fine and uniform in Figure 4c,d when the During the sintering, HfC, WC, and Mo dissolved and then reprecipitated as the solid solution (Ti, WC content was 24 and 32 wt %, respectively. The main reason for this was that as the WC content Hf, W, Mo)(C, N) to form the rim around the core—undissolved TiCN. When the WC content was 8 WC content was 24 and 32 wt %, respectively. The main reason for this was that as the WC content increased, the rim tended to be complete, which isolated the direct contact of the TiCN and, in turn, and 16 wt %, there were some big size dark phases (marked by circles in Figure 4a,b) which made the increased, the rim tended to be complete, which isolated the direct contact of the TiCN and, in turn, microstructure uneven. In contrast, the microstructure was fine and uniform in Figure 4c,d when the inhibited the growth of TiCN. In addition, there were some white dots on the fracture surfaces inhibited the growth of TiCN. In addition, there were some white dots on the fracture surfaces (marked WC content was 24 and 32 wt %, respectively. The main reason for this was that as the WC content (marked by the red arrows in Figure 4) and they decreased gradually as the WC content increased. by the red arrows in Figure 4) and they decreased gradually as the WC content increased. Especially increased, the rim tended to be complete, which isolated the direct contact of the TiCN and, in turn, Especially when the WC content was 32 wt % (in Figure 4d), the white dots were very few, which when the WC content wasof 32TiCN. wt %In (in Figurethere 4d), were the white dots were very which could also inhibited the growth addition, some white dots on the few, fracture surfaces could also be validated in Figure 2d. According to our previous finding [14], the white dots were HfC (marked by the red arrows in Figure 4) and they decreased gradually as the WC content increased. be validated in Figure 2d. According to our previous finding [14], the white dots were HfC particles. particles. Therefore, these indicated that the increase of WC content could promote the process of Especially when the WC content was 32 wt % (in Figure 4d), the white dots were very few, which Therefore, these indicated that the increase of WC content could promote the process of HfC to form a HfC to form a solid solution and that HfC formed a solid solution more easily with WC than with could also be validated in Figure 2d. According to our previous finding [14], the white dots were HfC solid solution and that HfC formed a solid solution more easily with WC than with TiCN. Besides, HfC particles. Therefore, these indicated that the increase of WC content could promote the process of TiCN. Besides, HfC particles locating at grain boundaries can play a very good pinning role for particlesHfC to form a solid solution and that HfC formed a solid solution more easily with WC than with locating at grain boundaries can play a very good pinning role for improving the mechanical improving the mechanical properties of the cermet. In addition, there were some pores (marked by properties of the cermet. addition, thereat were some pores (marked thegood yellow arrows Figure 4) TiCN. Besides, HfC In particles locating grain boundaries can play a by very pinning role infor the yellow arrows in Figure 4) in the fracture surface. These pores were composed of the micro‐void in the fracture surface. These pores were composed of the micro-void left by the pull-out grains in improving the mechanical properties of the cermet. In addition, there were some pores (marked by left by the pull‐out grains in the fracture process and the pore formation in the sintering process. The the yellow arrows in Figure 4) in the fracture surface. These pores were composed of the micro‐void the fracture process and the pore formation in the sintering process. The pull-out effect of grains pull‐out effect of grains was advantageous to improve the mechanical properties of cermets, while left by the pull‐out grains in the fracture process and the pore formation in the sintering process. The was advantageous to improve the mechanical properties of cermets, while the pore formation in the the pore formation in the sintering process was harmful to the mechanical properties of cermets. pull‐out effect of grains was advantageous to improve the mechanical properties of cermets, while sintering process was harmful to the mechanical properties of cermets. 0
2
4
6
8
10
the pore formation in the sintering process was harmful to the mechanical properties of cermets.
Figure 4. Cont.
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Figure 4. Fracture morphologies of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials with different WC
Figure 4. Fracture morphologies of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials with different 0.7N0.3‐HfC‐8 wt % WC (W8); (b) TiC 0.7N0.3‐HfC‐16 wt % WC (W16); (c) TiC0.7N0.3‐HfC‐ contents: (a) TiC WC contents: (a) TiC0.7 N0.3 -HfC-8 wt % WC (W8); (b) TiC0.7 N0.3 -HfC-16 wt % WC (W16); 0.7N0.3‐HfC‐32 wt % WC (W32). 24 wt % WC (W24); (d) TiC (c) TiC0.7 N0.3 -HfC-24 wt % WC (W24); (d) TiC0.7 N0.3 -HfC-32 wt % WC (W32). 3.2. Effects of WC Content on the Relative Density and Mechanical Properties of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo Cermets
3.2. Effects of WC Content on the Relative Density and Mechanical Properties of TiC0.7 N0.3 -HfC-WCNi-Mo Cermets Figure 5 presents the relative density and mechanical properties of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials with different WC contents. With the WC content increasing from 8 to 32 wt %,
Figure 5 presents the relative density and mechanical properties of TiC0.7 N0.3 -HfC-WC-Ni-Mo the relative density increased from (99.02 ± 0.03)% to (99.73 ± 0.02)%, the Vickers hardness increased cermet from 17.79 ± 0.30 to 21.06 ± 0.22 GPa, the flexural strength increased from 1042.61 ± 21 to 1270.56 ± 20 tool materials with different WC contents. With the WC content increasing from 8 to 1/2. The improvement 32 wt %,MPa, and the fracture toughness increased from 7.82 ± 0.37 to 9.47 ± 0.31 MPa∙m the relative density increased from (99.02 ± 0.03)% to (99.73 ± 0.02)%, the Vickers hardness of the relative density and Vickers hardness was mainly due to the wettability of Ni between WC increased from 17.79 ± 0.30 to 21.06 ± 0.22 GPa, the flexural strength increased from 1042.61 ± 21 being much better than that of Ni between TiCN. Better wettability can improve the sintering to 1270.56 ± 20 MPa, and the fracture toughness increased from 7.82 ± 0.37 to 9.47 ± 0.31 MPa·m1/2 . property of the material, so better densification and hardness were obtained. Therefore, the higher The improvement of the relative density and Vickers hardness was mainly due to the wettability of the content of WC was, the higher relative density and hardness of the material was. Besides, the Ni between WC being much better than that of Ni between TiCN. Better wettability can improve the reduction of flaws promoted the improvement of the relative density of materials. In addition, the sintering property of the material, so better densification and hardness were obtained. Therefore, fine microstructure was also benefit for the enhancement of hardness. W32 had the best hardness of 21.06 ± 0.22 GPa, which was higher than the value of 19.4 GPa reported in TiC 0.7N 0.3‐20 wt % HfC‐Ni‐ the higher the content of WC was, the higher relative density and hardness of the material was. Besides, Co cermet [14] and higher than the value of 17.54 GPa reported in TiCN‐WC‐Mo 2C‐Ni‐Mo cermet [2]. the reduction of flaws promoted the improvement of the relative density of materials. In addition, For the flexural strength, it increased with the increase of WC content, which can be explained the fine microstructure was also benefit for the enhancement of hardness. W32 had the best hardness by the Griffith‐Orowan equation [21]: of 21.06 ± 0.22 GPa, which was higher than the value of 19.4 GPa reported in TiC0.7 N0.3 -20 wt % 1/2 （2 EPof/ 17.54 L） HfC-Ni-Co cermet [14] and higher than the value GPa reported in TiCN-WC-Mo2 C-Ni-Mo cermet [2]. where E, P, and L represent the Young’s modulus, plastic deformation work due to crack stretching, Forand the length of the crack, respectively. The Young’s modulus values of TiC, TiN, HfC, and WC are the flexural strength, it increased with the increase of WC content, which can be explained by 510, 350, 470, and 731 GPa [22], respectively. E(WC) is much greater than E(TiC), E(TiN), and E(HfC). the Griffith-Orowan equation [21]: Therefore, the flexural strength increased with the increase of WC content. Meanwhile, the improved σ = (2EP/πL)1/2 flexural strength also benefited from the increase of grain bonding strength and the decrease of the
where E,weak light gray phase. When the material was subjected to external forces, the material with higher P, and L represent the Young’s modulus, plastic deformation work due to crack stretching, grain bonding strength would easily succumb to transgranular fracture. At this point, more fracture and the length of the crack, respectively. The Young’s modulus values of TiC, TiN, HfC, and WC energy would be consumed. Besides, the increase of the solid solution was also advantage to the are 510, 350, 470, and 731 GPa [22], respectively. E(WC) is much greater than E(TiC) , E(TiN) , and E(HfC) . flexural strength. W32 had the best flexural strength of 1270.56 ± 20 MPa, which was higher than the Therefore, the flexural strength increased with the increase of WC content. Meanwhile, the improved value of 1018.04 MPa reported in TiC 0.7N0.3‐20 wt % HfC‐Ni‐Co cermet [14]. flexural strength also benefited from the increase of grain bonding strength and the decrease of the As for fracture toughness, it increased with the increase of WC content. The solubility of WC in Ni is higher than that of TiC in Ni [22]. The higher solubility was favorable for the toughness of the weak light gray phase. When the material was subjected to external forces, the material with higher material. Also, the increase of grain bonding strength could efficiently inhibit crack propagation, so grain bonding strength would easily succumb to transgranular fracture. At this point, more fracture energy would be consumed. Besides, the increase of the solid solution was also advantage to the flexural strength. W32 had the best flexural strength of 1270.56 ± 20 MPa, which was higher than the value of 1018.04 MPa reported in TiC0.7 N0.3 -20 wt % HfC-Ni-Co cermet [14]. As for fracture toughness, it increased with the increase of WC content. The solubility of WC in Ni is higher than that of TiC in Ni [22]. The higher solubility was favorable for the toughness of
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the material. Also, the increase of grain bonding strength could efficiently inhibit crack propagation, Materials 2018, 11, x FOR PEER REVIEW 7 of 9 so the fracture toughness increased. In addition, the uneven distribution of grains (as shown in Materials 2018, 11, x FOR PEER REVIEW 7 of 9 Figure 4a,b) lead to the lower fracture toughness of W8 and W16 cermets. The reduction of the weak the fracture toughness increased. In addition, the uneven distribution of grains (as shown in Figure light4a,b) lead to the lower fracture toughness of W8 and W16 cermets. The reduction of the weak light gray phase was also advantageous to the improvement of the fracture toughness. W32 had the the fracture toughness increased. In addition, the uneven distribution of grains (as shown in Figure best gray phase was also advantageous to the improvement of the fracture toughness. W32 had the best fracture toughness of 9.47 ± 0.31 MPa·m1/2 , which was higher than the value of 8.6 MPa·m1/2 4a,b) lead to the lower fracture toughness of W8 and W16 cermets. The reduction of the weak light reported in TiC0.7 N0.3 -20 wt % HfC-Ni-Co1/2cermet [14], indicating that the formation of1/2a reported mass of solid fracture toughness of 9.47 ± 0.31 MPa∙m , which was higher than the value of 8.6 MPa∙m gray phase was also advantageous to the improvement of the fracture toughness. W32 had the best 1/2, which was higher than the value of 8.6 MPa∙m 1/2 reported in TiC 0.7N 0.3‐20 wt % HfC‐Ni‐Co cermet [14], indicating that the formation of a mass of solid solution solution can improve the fracture toughness. In order to further determine the toughening mechanisms fracture toughness of 9.47 ± 0.31 MPa∙m can improve the fracture toughness. In order to further determine the toughening mechanisms that in TiC 0.7 N 0.3 ‐20 wt % HfC‐Ni‐Co cermet [14], indicating that the formation of a mass of solid solution that operated in TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool material, an SEM micrograph of the crack operated in TiC N0.3‐HfC‐WC‐Ni‐Mo an SEM micrograph of the bridging crack in can improve the fracture toughness. In order to further determine the toughening mechanisms that propagation path is 0.7 exhibited in Figure 6.cermet There tool werematerial, mainly crack deflection and crack propagation path is exhibited in Figure 6. There were mainly crack deflection and crack bridging in operated in TiC 0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool material, an SEM micrograph of the crack TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials. In the process of crack propagation, crack deflection TiC 0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials. In the process of crack propagation, crack deflection propagation path is exhibited in Figure 6. There were mainly crack deflection and crack bridging in and crack bridging can consume more crack propagation energy, so the crack deflection and crack and crack bridging can consume more crack propagation energy, so the crack deflection and crack TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials. In the process of crack propagation, crack deflection bridging were advantageous to the improvement of the fracture toughness of the cermet. bridging were advantageous to the improvement of the fracture toughness of the cermet. and crack bridging can consume more crack propagation energy, so the crack deflection and crack bridging were advantageous to the improvement of the fracture toughness of the cermet. 21.5 22.0 21.0 21.5
Vickers hardness (GPa) Vickers hardness (GPa)
99.8 99.6
22.0
(a) (a)
19.5 20.0 19.0 19.5
99.4 99.2
18.5 19.0 18.0 18.5
99.2 99.0 99.0 98.8 98.8
8 8
1400
Flexural strength (MPa) Flexural strength (MPa)
1400 1350 1350 1300
16
24
WC16content /wt% 24 WC content /wt%
17.5 18.0 17.0 17.5
32 32
(c) (c)
8 8
10.5 10.5 10.0
(d) (d)
16
24
WC16content /wt% 24 WC content /wt%
32 32
9.5 9.0
1250 1200
9.0 8.5
1200 1150
8.5 8.0
1150 1100
8.0 7.5
1100 1050
1000
17.0
10.0 9.5
1300 1250
1050 1000
(b) (b)
20.5 21.0 20.0 20.5
99.6 99.4
Fracture toughness (MPa m) 1/2) Fracture toughness (MPa m1/2
Relative density Relative density (%)(%)
99.8
8
16
24 /24 wt%
WC 16content WC content /wt%
7.5 7.0
32
7.0
8
16
24
32
WC wt% 8 16 content /24 32 WC content / wt% Figure 5. Relative density and mechanical properties of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool 8
32
Figure 5. Relative density and mechanical properties of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials with different WC contents: (a) relative density; (b) Vickers hardness; (c) flexural strength; Figure 5. Relative density and mechanical properties of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials with different WC contents: (a) relative density; (b) Vickers hardness; (c) flexural strength; (d) fracture toughness. materials with different WC contents: (a) relative density; (b) Vickers hardness; (c) flexural strength; (d) fracture toughness. (d) fracture toughness.
Figure 6. SEM micrograph of crack propagation of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials. Figure 6. SEM micrograph of crack propagation of TiC0.7N0.3‐HfC‐WC‐Ni‐Mo cermet tool materials.
Figure 6. SEM micrograph of crack propagation of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials.
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4. Conclusions TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials with different WC content were sintered at 1450 ◦ C by hot pressing sintering technology. Effects of WC content on the microstructure and mechanical properties of TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials were investigated. The conclusions were as follows: (1)
(2)
(3)
TiC0.7 N0.3 -HfC-WC-Ni-Mo cermets were mainly composed of TiC0.7 N0.3 , Ni, and (Ti, Hf, W, Mo)(C, N). There were three phases: a dark phase, a gray phase, and a light gray phase. The dark phase was the undissolved TiC0.7 N0.3 , the gray phase was the solid solution (Ti, Hf, W, Mo)(C, N) poor in Hf, W, and Mo, and the light gray phase was the solid solution (Ti, Hf, W, Mo)(C, N) rich in Hf, W, and Mo. The solid solution (Ti, Hf, W, Mo)(C, N) resulted from the dissolution-reprecipitation process. With the WC content increasing, the grain bonding strength increased, which can restrain the crack propagation and then improve the fracture toughness of the cermet. In addition, the increase of WC content could promote the process of HfC to form a solid solution. Also, the HfC formed a solid solution more easily with WC than with TiCN. The relative density, hardness, flexural strength, and fracture toughness of the TiC0.7 N0.3 -HfC-WC-Ni-Mo cermet tool materials increased with the increase of the WC content in this investigation. When the content of WC was 32 wt %, the cermet obtained the optimal relative density and comprehensive mechanical properties: their values were (99.73 ± 0.02)%, 21.06 ± 0.22 GPa, 1270.56 ± 20 MPa, and 9.47 ± 0.31 MPa·m1/2 , respectively.
Author Contributions: J.S. and J.G. conceived and designed the experiments; J.G. performed the experiments; J.S. and J.G. analyzed the data; M.L. contributed reagents/materials/analysis tools; J.S. and J.G. wrote the paper. Funding: This research was funded by National Natural Science Foundation of China grant number 51405326 and 51575375, and by Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi grant number 2014122. Conflicts of Interest: The authors declare no conflict of interest.
References 1. 2. 3.
4. 5. 6. 7. 8.
9.
Liu, C.; Lin, N.; He, Y.H. Influence of Mo2 C and TaC additions on the microstructure and mechanical properties of Ti(C, N)-based cermets. Ceram. Int. 2016, 42, 3569–3574. [CrossRef] Yin, Z.B.; Yan, S.Y.; Xu, W.W.; Yuan, J.T. Microwave sintering of Ti(C, N)-based cermet cutting tool material. Ceram. Int. 2018, 44, 1034–1040. [CrossRef] Zhao, Y.J.; Zheng, Y.; Li, Y.; Zhou, W.; Zhang, G.T.; Zhang, J.J.; Xiong, W.H. Microstructure and performance of graded Ti(C, N)-based cermets modified by nitriding treatment during different sintering stages. Int. J. Refract. Met. Hard Mater. 2017, 62, 1–8. [CrossRef] Wu, Y.M.; Xiong, J.; Guo, Z.X.; Yang, M.; Chen, J.Z.; Xiong, S.J.; Fan, H.Y.; Luo, J.J. Microstructure and fracture toughness of Ti(C0.7 N0.3 )-WC-Ni cermets. Int. J. Refract. Met. Hard Mater. 2011, 29, 85–89. [CrossRef] Vikas Verma, B.V.; Kumar, M. Processing of TiCN-WC-Ni/Co cermets via conventional and spark plasma sintering technique. Trans. Indian Inst. Met. 2017, 70, 843–853. [CrossRef] Park, c.; Nam, S.; Kang, S. Enhanced toughness of titanium carbonitride-based cermets by addition of (Ti, W)C carbides. Mat. Sci. Eng. A 2016, 649, 400–406. Park, C.; Kang, S. Carbide/binder interfaces in Ti(CN)-(Ti, W)C/(Ti, W)(CN)-based cermets. J. Alloy. Compd. 2016, 657, 671–677. Sun, W.C.; Zhang, P.; Li, P.; She, X.L.; Zhang, Y.J.; Chen, X.G. Effect of short carbon fibre concentration on microstructure and mechanical properties of TiCN-based cermets. Adv. Appl. Ceram. 2016, 115, 216–223. [CrossRef] Dong, G.B.; Xiong, J.; Chen, J.Z.; Guo, Z.X.; Wan, W.C.; Yi, C.H.; Chen, H.S. Effect of WC on the microstructure and mechanical properties of nano Ti(C, N)-based cermets. Int. J. Refract. Met. Hard Mater. 2012, 35, 159–162. [CrossRef]
Materials 2018, 11, 968
10.
11. 12. 13.
14.
15.
16.
17.
18.
19. 20. 21.
22.
9 of 9
Qu, J.; Xiong, W.H.; Ye, D.M.; Yao, Z.H.; Liu, W.J.; Lin, S.J. Effect of WC content on the microstructure and mechanical properties of Ti(C0.5 N0.5 )-WC-Mo-Ni cermets. Int. J. Refract. Met. Hard Mater. 2010, 28, 243–249. [CrossRef] Wang, J.; Liu, Y.; Zhang, P.; Peng, J.C.; Ye, J.W.; Tu, M.J. Effect of WC on the microstructure and mechanical properties in the Ti(C0.7 N0.3 )-xWC-Mo2 C-(Co, Ni) system. Int. J. Refract. Met. Hard Mater. 2009, 27, 9–13. Mun, S.; Kang, S. Effect of HfC addition on microstructure of Ti(CN)-Ni cermet system. Powder Metall. 1999, 42, 251–256. [CrossRef] Song, J.P.; Jiang, L.K.; Liang, G.X.; Gao, J.J.; An, J.; Cao, L.; Xie, J.C.; Wang, S.Y.; Lv, M. Strengthening and toughening of TiN-based and TiB2 -based ceramic tool materials with HfC additive. Ceram. Int. 2017, 43, 8202–8207. [CrossRef] Gao, J.J.; Song, J.P.; Liang, G.X.; An, J.; Cao, L.; Xie, J.C.; Lv, M. Effects of HfC addition on microstructures and mechanical properties ofTiC0.7 N0.3 -based and TiC0.5 N0.5 -based ceramic tool materials. Ceram. Int. 2017, 43, 14945–14950. [CrossRef] China State Bureau of Technological Supervision. Chinese National Standards-Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics)—Test Method for Flexural Strength of Monolithic Ceramics at Room Temperature; Chinese Standard Publishing House: Beijing, China, 2006. An, J.; Song, J.P.; Liang, G.X.; Gao, J.J.; Xie, J.C.; Cao, L.; Wang, S.Y.; Lv, M. Effects of HfB2 and HfN additions on the microstructures and mechanical properties of TiB2 -based ceramic tool materials. Materials 2017, 10, 461. [CrossRef] [PubMed] Song, J.P.; Cao, L.; Jiang, L.K.; Liang, G.X.; Gao, J.J.; Li, D.X.; Wang, S.Y.; Lv, M. Effect of HfN, HfC and HfB2 additives on phase transformation, microstructure and mechanical properties of ZrO2 -based ceramics. Ceram. Int. 2018, 44, 5371–5377. [CrossRef] China State Bureau of Technological Supervision. Chinese National Standards-Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics)—Test Method for Hardness of Monolithic Ceramics at Room Temperature; Chinese Standard Publishing House: Beijing, China, 2009. Manoj Kumar, B.V.; Bikramjit, B. Mechanisms of material removal during high temperature fretting of TiCN-Ni based cermets. Int. J. Refract. Met. Hard Mater. 2008, 26, 504–513. [CrossRef] Zhou, S.Q.; Zhao, W.; Xiong, W.H.; Zhou, Y.N. Effect of Mo and Mo2 C on the microstructure and properties of the cermets based on Ti(C, N). Acta Metall. Sin. 2008, 21, 211–219. [CrossRef] Liu, N.; Zhao, C.L.; Zhao, X.Z.; Zhou, F.Y.; Hu, Z.H.; Cui, K.; Xu, W.B. The influence of the adding contents of TiN and WC on the microstructure and mechanical properties of Ti(C, N)-based cermets. Cem. Carbide 1994, 11, 13–16. Li, R.J. Ceramic—Metal Composite Materials, Seconded; Metallurgical Industry Press: Beijing, China, 2004. © 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/).
