mechanical properties, corrosion behavior, and bioactivity of ...

262 Adv. Mater. Sci. 30 (2012) 262-266 Rev.

A. Nur Maizatul Shima, B.J. Shamsul and D. Mohd Nazree

MECHANICAL PROPERTIES, CORROSION BEHAVIOR, AND BIOACTIVITY OF COMPOSITE METAL ALLOYS ADDED WITH CERAMIC FOR BIOMEDICAL APPLICATIONS Nur Maizatul Shima Adzali1, Shamsul Baharin Jamaludin2 and Mohd Nazree Derman3 1 Schools of Materials Engineering, University Malaysia Perlis (UNIMAP), Kompleks Pusat Pengajian Taman Muhibah, Jejawi, 02600, Arau, Perlis, Malaysia 2 Sustainable Engineering Research Cluster, University Malaysia Perlis, Malaysia 3 Institute of Nano Electronic Engineering, University Malaysia Perlis, Malaysia

Received: February 29, 2012 Abstract. In recent years, the development and use of biomaterials are expected to continuously increase over the coming decades as a result of ageing populations in the world. The biomaterials community is producing new and improved implant materials and techniques to meet this demand. A lot of new materials that have been produced in biomaterials field such as cobalt, magnesium, and titanium based alloys reinforced with ceramic. Many types of ceramics that suitable as reinforcement for these alloys such as bioactive glass, hydroxyapatite (HA), wollastonite, calcium pyrophosphate, boron carbide, silicium nitride, fluoroapatite (FA) and so many others. This paper reviews the research works carried out in the field of composite metal alloys reinforced with ceramic with special reference to their mechanical properties, corrosion and also bioactivity behavior.

J b[TkZ bY b S Na V TbR aR[Ta UdRN RVa N[P R good biotolerance and high corrosion resistance. Variety of materials including metals, polymers, The most of Co-based alloys have been fabricated ceramics and composites with the appropriate by using casting technique. This technique has physical properties and biocompatibility are chosen provided lower initial costs. However, noticeable for the fabrication of biomaterials. Metallic materials restrictions that encountered with casting are coarse are commonly used for load bearing implants and grain size, non-uniform microstructural segregation internal fixation devices [1]. Current metallic and also lower tensile and fatigue strength. biomaterials such as cobalt based alloys (primarily Fabrication via hot forging and powder metallurgy Co-Cr-Mo), austenitic stainless steels, titanium and are expected to give better properties [2]. The rigidity titanium base alloys and magnesium based alloys of sintered Co based alloy is significantly lower than are the common materials used in orthopedics. analogue cast alloy, which is very important Recently, cobalt based alloys have become one requirement from the point of view of bone restoration of the important metallic biomaterials because it process. exhibites low levels of corrosion and this alloy Most of the research reports that pure porous remains as a fixture in orthopedic surgery to this Co based alloys have a lower resistance to pitting day. Co based alloys are well known for their high and crevice corrosion than solid materials [3-5]. It Corresponding author: Nur Maizatul Shima Adzali, e-mail: [email protected]

1. INTRODUCTION

h( (3 c N[PR Da b f5R[a R5

a

Mechanical properties, corrosion behavior, and bioactivity of composite metal alloys added with... happened because of the increased contact area of their surface with the electrolyte, which results in the polarization current density being shifted towards higher values. In general, corrosion resistance increases with increasing the density of material, which can be realized by introducing appropriate additives such as ceramic [6]. In particular, the second very important group of biomaterials is ceramics, with much attention has already paid to calcium based biomaterials like hydroxyapatite (HAP with chemical formula Ca 10 (PO 4 ) 6 (OH) 2 ), due to their excellent biocompatibility, structural and chemical similarity with bone mineral compositions [7]. Other bioceramics may be bioinert (alumina, zirkonia), bioresorbable (tricalcium phosphate), bioactive (hydroxyapatite, bioactive glasses, and glass ceramics), or porous for tissue in growth (hydroxyapatite coating and bioglass coating on metallic materials) [8-10]. As reported by Navarro et al. [11], the application of this ceramic material as bone substitutes started around the 1970s and has mainly used as bone defect fillers. HAP is highly stable in body fluids, interacts with bone tissue upon implantation and enhances bone cell proliferation. Little attention has been focused on biocomposite material based on metal alloys matrix filled with ceramic, but the results shows that this bio-composite is a promising candidate for implants to improve bioactivity, mechanical properties and corrosion properties [6,12,13]. Therefore, this research presents the effect of ceramic addition in metal alloy produced by various method. Further studies are still of necessity for metal alloys to achieve significant improvement in both mechanical properties and corrosion resistance.

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Table 1. The comparison of elastic modulus values of bone and investigated materials (GPa) [14]. Sample

Elastic modulus (GPa)

Bone Cast Co-Cr-Mo alloy Sintered Co-Cr-Mo alloy Composite with 10% volume addition of: Ca2P207 (calcium pyrophosphate) B4C (Boron caribide) Si3N4 (Silicon Nitride)

3.14 240 8.1

37 12 3.8

strength and yield point values are comparable with properties of cast Co-Cr-Mo alloys. The influence of the other two additives (boron carbide and silicon nitride) on composite properties was insignificant. The influence of these three additives on the rigidity of composites is shown in Table 1, with the values of elastic modulus of the samples are lower than analogous cast alloys. This characteristic is important for implants biomechanics characteristic. The rigidity of metallic prostheses is usually much higher than bone. Therefore, the load is mainly carried by the implant. Their results show that these composites can be alternative materials for biomedical applications. Another successful material that can act as additive to Co based alloys is bioglass [6], which the composite has been prepared by powder metallurgy method. The addition of 5 wt.%, 10 wt.%, and 15 da SOVTY N aa UR5 j5 j ZNaV e N dRY Y as applying the rotary cold repressing and heat

2. Co BASED ALLOYS COMPOSITES The application of Co-Cr-Mo alloys as femoral components have been widely used due to their mechanical properties, good wear and corrosion resistances as well as biocompatibility [14]. Gradzka-Dahlke et al. [14] have studied the influence of ceramic additives such as calcium pyrophosphate, boron carbide and silicon nitride on mechanical properties of the composite Co-Cr-Mo alloy. These composites successfully fabricated via powder metallurgy method. The results showed that the effect of examined fillers were different. The most advantageous properties were obtained for the composite with calcium pyrophosphate, with the highest compactibility and good mechanical properties compared to two others. The compressive

Fig. 1. SEM microstructures of the specimens: (a) ]bR5 j5 j NY Yf1 O NY YfdV a U+da S bioglass; (c) alloy with 10 wt.% of bioglass; (d) alloy with 15 wt.% of bioglass. Reprinted with permisV[S ZL ,Mh( /7YRc V R

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Fig. 2. Compressive stress-strain curves for AZ91 (magnesium alloys) and AZ91-20FA (magnesium reinforced with 20 wt.% FA) samples. Replotted from [13].

Fig. 3. Tafel plot for sample AZ91 (magnesium alloys) and AZ91-20FA (Magnesium alloys with 20 wt.% FA). Replotted from [13].

treatment have a significant influence on the microstructure, mechanical properties and corrosion resistance of the composite in comparison with the 5 j5 j V [a RR NY Yf 8V T Ud a UR microstructure of the composites after heat treatment, which composed of the matrix alloy in grey areas, bioglass particle (white regions) and pores (dark regions). These elements are distributed uniformly throughout the material structure.

environment containing various anions such as Cl-, HCO3-, HPO42-, cations such as Na+, K+, Ca2+, Mg2+, organic substances, and dissolved oxygen [16-18]. According to Yoshiaki et al. [19], Bishop et al. [20], and Sameljuk et al. [21], the incorporation of second reinforcing phase into metal matrix not also enhances the physical and mechanical properties SNZNa RV NYObaV aNY PN[NY a Ra URZNa RV NY k corrosion behaviour. It was reported by Oksuita et al. [6] and GradzkaDahkle et al. [14] that the addition of filler to Co-CrMo based composite can enhance the corrosion resistance. Although Co-Cr based alloys shows low level of corrosion, however, when implanted into the human body, the metal-in-metal joint will experience tribocorrosion, a form of metal degradation, which may lead to the release of metals ions into the body [22]. So, the addition of Ca and phosphate from hydroxyapatite is known to reduce the susceptibility of Co-Cr-Mo alloys to corrosion [6].Thus bioceramic as well as HAP play a twin role both in preventing the release of metal ions (rendering it more corrosion resistant) and also in making the metal surface bioactive [17]. In the research conducted by Razavi et al. [13], they have found that the addition of fluoroapatite (FA) nanoparticle reinforcements to magnesium alloys has reduced the corrosion rate (Fig. 3). As seen in Fig. 3, the corrosion resistance of AZ91-20FA is higher than pure magnesium alloys (AZ91), which confirmed by the values of their corrosion currents (Icorr) and corrosion potentials (Ecorr).

3. Mg BASED ALLOYS COMPOSITES Razavi et al. [13] presented new nanocomposite made of AZ91 magnesium alloy added with nano particles of fluoroapatite (FA) which has been successfully prepared by blending-pressingsintering method. This composite is more suitable for large degradable implants in load bearing applications compared to a biomaterial with lower compressive yield strength than natural bone [13]. This composite was proved to have good mechanical properties and low corrosion rate. Fig. 2. shows the results for compressive strength for AZ91-20FA and AZ91. AZ91-20FA have higher compressive strength c NY bR -i BN PZ]NR a3K/ ..i+ BN The AZ91-20FA sample seemed to be in higher agreement than AZ91 magnesium alloy with the characteristics of the natural bone, having P Z]R V c Rf V RY aR[Ta U S) j . BNL+M

4. CORROSION AND BIOACTIVITY BEHAVIOR 4.1. Corrosion Corrosion occurred as a result of chemical and electrochemical reactions with its surrounding environment. Implants materials installed in human body are generally exposed to harsh aqueous

4.2. Bioactivity behavior Bioactivity test is an evaluation of apatite-forming on implant material in SBF (simulated body fluid). When a bioactive material is implanted in a animal

Mechanical properties, corrosion behavior, and bioactivity of composite metal alloys added with...

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Fig. 4. SEM microphotographs of all composite materials before and after immersion in SBF for various ]RV S a V ZR CR]V [a R dV a U]RZV V[S ZL ,Mh( 3 U V [TBbOY VUV [T

or human body, a thin layer rich in Ca and P forms on its surfaces. This apatite layer can connects this bioactive material to the living tissue. Materials of various kinds bind to living bone through this apatite layer which can be reproduced on their surfaces in SBF, and that apatite formed is very similar to the bone mineral in its composition and structure. As bioactivity increases, apatite forms on the material surface in a shorter time in proportion to this increase. The formation of this apatite layers have mostly been analyzed by thin film X-ray diffraction (TF-XRD) [23,24], fourier transformed infrared spectroscopy (FTIR) [25,26] and scanning electron microscopy coupled engergy dispersive X-ray spectroscopy (SEM/EDXA) [27]. Roumeli et al. [28] have studied about bioactivity behavior of SiO2j5NAj TATY N P RNZV P+ , SiO 2 , 35.6% CaO, and 12.8% MgO) and homogeneous mixtures of 75% HA/25% SiO2j5NAj MgO (75:25) and 50% HA/50% SiO2j5NAj TA (50:50) that were obtained by Transferred Arc Plasma (TAP) melting method. These composites were immersed in simulated body fluid (SBF) solution for various immersion periods of time. The results show that all materials showed the formation of an HCAp layer on top of every pellet. Both 50:50 and 75:25 composites show rather thick apatite layer (5-6 m), while pure glass pellet shows much thinner layer (1-2 m). The microstructure of these composites (Fig. 4) reveals for longer reaction times, the apatite layer covered a greater fraction of the pellet surface. As seen in Fig. 4, the apatite layer

consists of spherulitic apatite aggregates even after 6 days of immersion in SBF solution. The study about biomimetic apatite formation on a Co-Cr-Mo alloy by using wollastonite, bioactive glass or hydroxyapatite has been conducted by Cortes et al. [29]. This biomimetic method used to promote a bioactive surface on a Co-Cr-Mo alloy (F75). This metallic samples were chemically treated and immersed for 7 days in SBF solution on a bed of these three bioactive materials (wollastonite, bioactive glass and hydroxyapatite), followed by an immersion in 1.5 SBF for 7 or 14 days without bioactive system. As a results, the surface of all samples were formed a bonelike apatite layer, with wollastonite presented a higher rate of apatite formation. By using XRD, hydroxyapatite was detected only on the samples treated with wollastonite after 7 days of immersion. This proved that rate of apatite formation increases by using wollastonite.

5. CONCLUSION The composite metal alloys added with ceramic for biomedical applications were reviewed from the point of microstructure and mechanical properties and also corrosion and bioactivity behavior. Investigations about these composites have found ceramic as a additive can enhance the mechanical properties, reduce the corrosion rate, and accelerate the formation of an apatite layer on the surface, which provides improved protection for the metal based

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alloys matrix. Thus, we conclude that those composites can be good alternative materials for biomedical applications.

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