Mazlan Mohamad

Fabrication of 316L stainless steel parts by Injection Moulding for Biomedical Application using a Novel Binder

This paper focuses on the usage of a novel binder system base on palm oil product to produce sintered parts of stainless steel 316L produced by vertical injection molding technique for biomedical application. The stainless steel 316L powder was mixed using z-blade mixer with the thermoplastic binder system comprising of polyethylene, paraffin wax, stearic acid and palm stearin which was derived from palm oil at different volume percent (%). The feedstock then was studied in term of viscosity and shear rate using capillary rheometer. The feedstock was molded using vertical injection molding machine. After molding, the green molded part was immersed into the solvent to extract part of the binder system followed by sintering under vacuum atmosphere at the temperature of 1360°C. The physical and mechanical properties of the sintered part such as density, hardness, shrinkage, ultimate tensile strength and elongation were measured. Biocompatibility study of in vitro test using cell osteosarcoma MG-63 was observed and discussed.

Effect of Sintering Conditions on Mechanical Properties and Microstructure of Titanium Alloy Produced by Metal Injection Moulding (MIM)

Metal Injection Moulding (MIM) is an efficient method for high volume production of complex shape components from powders. The purpose of this study is to determine the sintering condition of titanium alloy (Ti6Al4V) tensile shape sample. In high temperature, Ti6Al4V will react with oxygen to form of titanium oxide (TiO2) which present a problem during sintering thus affected the mechanical properties and microstructure. This reaction can be avoided either by introducing argon gases or in vacuum condition. Ti6Al4V with binder formulation consist of polyethylene (PE), paraffin wax (PW), stearic acid (SA) and palm oil derivatives; palm stearin (PS) were mixed homogenously and injected to produce green compact. The binders then are removed and sintered at 1100 °C for 8 h. During sintering, the debound part is heated, thus allowing densification of the powder into a dense solid with the elimination of pores. It was expected that the impurity gas in argon had strong effects on aspects of the densification and properties. Samples of PE/PS formulation with argon added to the sintering atmosphere, experience density of 4.375g/cm3 and tensile strength stated at 1000.100MPa compared to samples in vacuum condition which do not show any significant increment with density of 3.943g/cm3 and tensile strength at 325.976MPa. PE/PW/SA samples of vacuum condition also show no improvement in sintered properties. However with additional argon flow the density can reach until 4.359g /cm3 and 940.823MPa of tensile strength. Ti-alloy sintered in argon exhibited better densification rate than in vacuum with high strength, better elongation and lower porosity. In argon, the powder particles became interconnected signifying densification was achieved due of non-reactive properties of inert gases that prevent undesirable chemical reactions from taking place.

Morphology Studies of Electrospun Lithium Iron Phosphate (LiFePO4)/Cellulose Acetate (CA) Fibers

This work was carried out as a preliminary study of electrospun LiFePO4/CA fibers. Cellulose acetate (CA) and LiFePO4 solutions were prepared separately using mixed solvent of acetone and water, prior to the electrospinning process. Then, electrospinning parameters including solution concentration, distance tip to collector, pump rate, and needle diameter size were optimized. Brunauer Emmett Teller (BET) was used to determine the surface area of CA fibers. Viscosity of CA solution was obtained by viscometer. LiFePO4/CA fibers were stabilized and carbonized at different temperature. The surface morphology and microstructure of the obtained LiFePO4/ CA fibers were then characterized using scanning electron microscope (SEM). In this work, it is shown that different electrospinning parameter, solution concentration and solution viscosity gives different fibers diameter and distribution. Moreover, the stabilization and carbonization temperature of LiFePO4/CA fibers may also affect the fibers microstructure.

Rheological Study of a Copper Feedstock

MIM technique is described in which allows for the production of highly porous metallic foams with porosity levels up to 90%. It makes use of the pressure built up by the decomposition of a foaming agent which is incorporated in a foamable precursor copper material obtained by powder compaction. A suitable behaviors feedstock that refers to its rheological is one of the key factors to ensure the successful of MIM technique and to predict failure, whether due to the binder component and compositions, powder loading or unsuitable process parameters. Potassium carbonate and polyethylene is added and were mixed homogeneously to form a copper feedstock. The rheological results in term of shear rate, shear stress, viscosity, melting rate and softening temperature which related to pseduoplastic behaviors have been conducted using a capillary rheometer (CFT-500D, Shimadzu) at various temperature and loads. The result has indicated that the viscosity of the feedstock is decreased with increasing shear rate thus proved the feedstock to be pseudoplastic.

Physical and Mechanical Properties of Sintered Titanium Alloy Produced through Metal Injection Molding (MIM) Process for Craniofacial Application

Metal injection molding (MIM) is capable of mass producing intricately shaped components. In recent years, this technology has been adopted in the electronic, computer, aerospace and medical industries. Titanium alloy (Ti6Al4V) is difficult to process because of its reactive nature and primarily because of problems with carbon and oxygen impurities. Even at low concentration, these interstitials can severely degrade the mechanical properties of titanium and its alloys. The main objective of this study is to develop a sintering condition that would eliminate problems with carbon and oxygen contamination and facilitate binder removal, thus enhance the sintering properties. Ti6Al4V with binder formulation consists of polyethylene (PE), paraffin wax (PW), stearic acid (SA) and palm oil derivatives; palm stearin (PS) were mixed homogeneously and injected to produce green compacts. The binders then were removed and sintering of injection molded material was conducted up to 1200 °C in vacuum atmosphere. The parts sintered at 1150 °C for 8 h exhibited among the highest tensile strength of 921.1 MPa while the elongation, density, porosity and hardness was 6.4%, 4.358 g/cm3, 3.16% and 320 HV respectively. This is the advantageous of additional argon flow during debinding , whereas the physical and mechanical properties were improved due to the impurity gas in argon that had strong effects on the aspects of densification and elimination of pores that turn the powder into a dense solid Ti6Al4V.

Effect of Solid Loading on the Physical Properties of the Sintered Inconel 718 Using Metal Injection Moulding (MIM)

Inconel 718 has been widely used as a super alloy in aerospace application due to the high strength at elevated temperatures, satisfactory oxidation resistance and heat corrosion resistance. In this study, the Inconel 718 with different solid loading (System A - 50/50 vol.% and System B - 60/40 vol.%) has been fabricated using high technology of Metal Injection Moulding (MIM) process due to the cost effective technique for producing small, complex and precision parts in high volume compared with conventional method through machining. Through MIM, the binder system is one of the most important criteria in order to successfully fabricate the Inconel 718. Even though, the binder system is a temporary, but failure in the selection and removal of the binder system will affect on the final properties of the sintered parts. Therefore, the binder system based on palm oil derivative which is palm stearin has been formulated and developed. The rheological studies of the mixture between the powder and binders system have been determined properly in order to be successful during injection into injection moulding machine. After moulding, the binder holds the particles in place. The binder system has to be removed completely through debinding step. During debinding step, solvent debinding and thermal pyrolysis has been used to remove completely of the binder system. The debound part is then sintered to give the required physical properties.