Injection Molded 316L Stainless Steel Research Articles

Antimicrobial activity of porous metal injection molded (MIM) 316L stainless steel by Zn, Cu and Ag electrodeposition

Porous 316L stainless steel samples were functionalized with electrodeposited zinc, copper, and silver coatings for antimicrobial activity against gram-positive bacteria Staphylococcus aureus (S. aureus). Porous stainless steel samples were created by combining metal injection molding (MIM) with a powder space holder (PSH) technique using sodium chloride (20 wt%) as a space holder material. Galvanostatic (0.10 A) electrodeposition was used for zinc, copper, and silver deposition, and antimicrobial activity of functionalized samples was evaluated using a touch test protocol with S. aureus. All electrodeposited samples completely prevented the growth of S. aureus. These results confirm that metal depositions only in the pores of the porous 316L were sufficient to inhibit the growth of S. aureus completely.

Determination of optimised solvent debinding parameters of injection moulded 316L stainless steel using Taguchi approach

Abstract Metal Injection Moulding (MIM) is widely utilized in various manufacturing industries due to its ability to produce near net shaped components in high volume without compromising surface finish and mechanical properties. Debinding is one of the most crucial phases in the MIM process, as it affects the final properties of the end product. The use of 316L SS is widespread especially in the medical industry, specifically for implants and metallic biomaterials due to its favourable combination of mechanical properties and biological consistency The present work deals with utilization of the Taguchi method to investigate the influence of solvent debinding parameters on the characteristics of injection moulded 316L stainless steel (316L SS) using thermoplastic rice starch binder as one of the binder components. In this study, the 316L SS powder along with a binder system consisting of Thermoplastic Rice Starch (TPRS), Polyethylene (PE), Palm Stearin (PS) and Stearic Acid (SA) were mixed for 1 hour at a speed of 50 rev/min and at a temperature of 150°C using a Z-blade mixer. The feedstock was then injection moulded using a vertical injection moulding machine with parameters of injection pressure, injection temperature and time and holding time of 7 bar, 160°C, 10 seconds and 25 seconds respectively. , this research was done utilizing the Taguchi approach to investigate the influence of solvent debinding parameters of injection molded 316L SS The effects of three solvent debinding parameters: solvent type, debinding time and debinding temperature were investigated to obtain the highest percentage of binder removal. The interactions of the parameters were laid out using the L 9 orthogonal array. It was found through ANOVA that solvent type had the most significant effects on solvent debinding, followed by debinding temperature and debinding time. The optimized solvent debinding parameters are solvent type of methanol, debinding temperature of 80°C and debinding time of 4 hours. The confirmation experiment however did not achieve the required range of expected result with a 3.80% error due to the unstable behaviour of the optimized solvent type, methanol.

Effect of waste rubber binder on sintered properties of 316L SS for metallic implant parts

This paper studies the influence of waste rubber binder on the properties of injection moulded 316L stainless steel. The new feedstock was formulated at volume fraction of 65% of metal powder and 35% of binder system. Powder with mean particle size of 45 μm was mixed with binder system and then successfully injection moulded. The samples were immersed in n-heptane for 5 hours at temperature of 60⁰C. Thermal debinding process was carried out to remove the remaining binders. The specimens were then sintered in vacuum condition at different temperature ranges of 1320⁰C to 1380⁰C. The properties of the sintered samples were evaluated. The sintered density recorded from 7.31 g/cm 3 to 7.62 g/cm 3 at 30 minutes and 60 minutes of soaking time. At temperature of 1360⁰C, the maximum tensile strength of 475.5 MPa attained and the highest hardness was obtained at 265 Hv. Keywords: waste rubber; injection moulded; feedstock; sintered density; tensile strength

Investigation of Boron Addition on Densification and Cytotoxicity of Powder Injection Molded 316L Stainless Steel Dental Materials

Powder injection molding (PIM) is a hybrid of powder metallurgy and plastic injection molding. It is used to develop metallic molded parts with intricate shapes and with improved properties compared with those offered by their wrought counterparts. PIM dental implants should exhibit biocompatibility, high density, good dimensional control, homogeneous properties and low manufacturing cost. In order to achieve these properties, the effect of boron (additive) addition on sintered density and of process effects on the biocompatibility of sintered implants was studied. In activated sintering, additives are used in small quantities to modify the sintering behavior of stainless steel. A constant amount of nanosize elemental boron (0–1.5 wt%) was admixed with 316L stainless steel and was compounded with complex binder to develop feedstocks using a z-blade mixer. Optimal solvent debinding parameters followed by an optimal sintering cycle played a vital role in the development of biocompatible and densified 316L stainless steel dental implants. Although all boron-containing formulations were injection-molded successfully, only PWA-0.5B-1230 samples were able to retain their shapes after sintering. It was concluded that 0.5 wt% addition of elemental boron favored the formation of 316L stainless steel with a sintered density of up to 98.5 % through the formation of a complex iron boride compound (B6Fe23) on the grain boundaries during the sintering process. The formation of a passive layer on the outer surface of implants was controlled using optimal sintering parameters. In in vitro analysis, the cytotoxicity assessment of sintered dental implants materials was determined using the direct and indirect contact techniques.

A Study on the Optimization of Solvent Debinding Process for Powder Injection Molded 316L Stainless Steel Parts

Optimization of solvent debinding process parameters for powder injection molded 316L stainless steel (SS) has been reported in this research work. Powder gas atomized (PGA) 316L SS was blended with a multicomponent binder in Z-blade mixer at 170°C ± 5°C for 90 minutes. Feedstock was successfully injected at temperature 170 ± 5°C. Injection molded samples were immersed in n-heptane for 2h, 4h, 6h and 8h at temperatures 50°C ,55°C and 60°C to extract the soluble binder components. Scanning electron microscope (SEM) results attested that soluble binder components were completely extracted from injection molded samples at temperature 55°C after 6h.

Effect of Zr, Nb and Ti Additions on Injection Molded 316L Stainless Steel: Microstructural, Mechanical Properties and Corrosion Resistance

The objective of this research is to investigate the effect of Zr, Nb and Ti additions on microstructural, mechanical and electrochemical properties of injection molded 316L stainless steel. The amount of additive powder plays a role in determining the sintered microstructure and all properties. In this study, 316L stainless steel powders used with the elemental Zr, Nb and Ti powders. The binders were completely removed from molded components by solvent and thermal debinding. The debinded samples were sintered at different temperature for 60 min. at different temperatures. Mechanical property, microstructural characterization and electrochemical property of the sintered samples were performed using tensile testing, hardness, optical, scanning electron microscopy and electrochemical experiments. Results of study showed that sintered 316L and 316L with additive powder samples exhibited high mechanical and corrosion properties in a physiological environment.

Effect of Zr, Nb and Ti addition on injection molded 316L stainless steel for bio-applications: Mechanical, electrochemical and biocompatibility properties

The research investigated the effect of Zr, Nb and Ti additions on mechanical, electrochemical properties and biocompatibility of injection molded 316L stainless steel. Addition of elemental powder is promoted to get high performance of sintered 316L stainless steels. The amount of additive powder plays a role in determining the sintered microstructure and all properties. In this study, 316L stainless steel powders used with the elemental Zr, Nb and Ti powders. A feedstock containing 62.5wt% powders loading was molded at different injection molded temperature. The binders were completely removed from molded components by solvent and thermal debinding at different temperatures. The debinded samples were sintered at 1350°C for 60min. Mechanical, electrochemical property and biocompatibility of the sintered samples were performed mechanical, electrochemical, SBF immersion tests and cell culture experiments. Results of study showed that sintered 316L and 316L with additives samples exhibited high corrosion properties and biocompatibility in a physiological environment.

Sintering behavior of 316L stainless steel micro–nanopowder compact fabricated by powder injection molding

The densification and grain growth behavior of powder injection molded 316L stainless steel micro–nanopowder were investigated in terms of microstructural development. The sintered density of the micro–nanopowder sample increased remarkably in the temperature range of 1000 to 1100°C due to the sintering effect of nanopowders which increased the number of grain boundaries acting as high material transport path. A near full density of 98% TD was obtained after sintering at 1100°C for 5h with the average grain size less than 10μm, indicating that there was no drastic grain growth. The presence of nanopowders in micro–nanopowder played decisive role in the entire sintering process by enhancing densification but suppressing grain growth. These effects open up the possibility of using micro–nanopowder feedstock to control the sintering behavior of powder injection molding products with full density and fine microstructure.

Role of Debinding to Control Mechanical Properties of Powder Injection Molded 316L Stainless Steel

316L stainless steel is widely used in various industries due to low cost, ease of availability and exceptional combination of mechanical properties along with corrosion resistance as compared to the other available metal alloys. In powder injection molding, debinding is very critical step and improper debinding can change the final properties dramatically. In the present study, affects of debinding on mechanical properties of powder injection molded 316L stainless steel were studied. The prepared feedstocks were molded according to MPIF 50 standard using vertical injection molding machine (KSA100). The plastic binder was removed at 450°C from the molded test samples using two different furnaces i.e. commercial and laboratory furnace followed by the sintering in vacuum, hydrogen, mixture of H2 and N2 (9:1) and nitrogen at 1325°C for 2hr with post sintering cooling rate 3°C/min . Test samples debound in commercially available furnace showed 97% densification and higher mechanical properties. The corrosion resistance was reduced due to presence of residual carbon during thermal debinding. The presence of carbon and formation of carbides and nitrides were confirmed by XRD and microstructural analysis. The results showed that the test samples debound in commercial furnace showed brittle behavior due to the presence of carbides and nitrides. Test samples sintered in N2 showed 96.3% density and tensile strength 751MPa. This value of strength is twice as compared to the sample debound in laboratory furnace followed by the sintering in vacuum. The achieved mechanical properties in vacuum sintered samples were comparable to the wrought 316L stainless steel (according to ASTM standard).

Effects of Sintering Temperature and Cooling Rate on Mechanical Properties of Powder Injection Molded 316L Stainless Steel

This research presents the effects of temperature and cooling rate on mechanical properties of powder injection molded 316L Stainless steel. Steel powder and binder were mixed together to produce the feedstock. The green samples were produced by injection molding and debinded. Brown test samples were sintered in vacuum at 1325°C, 1360°C and 1380°C for 2h with two heating and cooling rates 5°C/min and 10°C/ min. The test samples sintered at 1325°C achieved maximum sintered density. The higher cooling rate improved the strength of the sintered test samples. The maximum sintered density of 96% and tensile strength of 503MPa was achieved and these results are comparable to the wrought 316L stainless steel (according to ASTM standard).

Effect of boron addition on injection molded 316L stainless steel: Mechanical, corrosion properties and in vitro bioactivity

The research was investigated the effect of boron additions on sintering characteristics, mechanical, corrosion properties and biocompatibility of injection molded austenitic grade 316L stainless steel. Addition of boron is promoted to get high density of sintered 316L stainless steels. The amount of boron plays a role in determining the sintered microstructure and all properties. In this study, 316L stainless steel powders have been used with the elemental NiB powders. A feedstock containing 62.5 wt% powders loading was molded at different injection molded temperature. The binders were completely removed from molded components by solvent and thermal debinding at different temperature. The debinded samples were sintered at different temperature for 60 min. Mechanical property, microstructural characterization and electrochemical property of the sintered samples were performed using tensile testing, hardness, optical, scanning electron microscopy and electrochemical corrosion experiments. Sintered samples were immersed in a simulated body fluid (SBF) with elemental concentrations that were comparable to those of human blood plasma for a total period of 15 days. Both materials were implanted in fibroblast culture for biocompatibility evaluations were carried out. Results of study showed that sintered 316L and 316L with NiB addition samples exhibited high mechanical and corrosion properties in a physiological environment. Especially, 316L with NiB addition can be used in some bioapplications.

Effects of cooling rate on mechanical properties and corrosion resistance of vacuum sintered powder injection molded 316L stainless steel

This study presents the results of corrosion behavior of powder injection molded 316L stainless steel parts sintered in vacuum. The feedstocks of metal powder and plastic binder were prepared and their viscosity was measured. Green samples were injection molded and binder was removed from the green parts. Brown test parts were sintered at 1325°C with heating rate of 5°C/min and 10°C/min for 2h followed by the same cooling rate. Corrosion response of the sintered test samples was measured by weight loss method in Ringer's Solution of pH 7.4 for 15 days. The test samples using cooling rate 10°C/min showed higher mechanical properties and improved corrosion resistance compared to those sintered at low heating and cooling rate. High cooling rate reduced the evaporation of Cr and developed passive chromium oxide layer on the test samples resulting improved corrosion resistance.

Binder Removal from Powder Injection Molded 316L Stainless Steel

Binder Removal from Powder Injection Molded 316L Stainless Steel

Single Step of Binder Thermal Debinding and Sintering of Injection Moulded 316L Stainless Steel

Metal injection moulding was performed with gas atomized 316L stainless steel powders. Feedstocks were prepared using a paraffin wax/polyethylene/stearic acid binder system and subsequently molded into tensile bar specimens. Solvent extraction done at 80○C has shortened the debinding process to 30 minute. Single step of thermal binder debinding and sintering was done in a vacuum furnace. Sintering at 1380○C has reduced the porosity and associated with grain growth that result in an increase in ultimate tensile strength to 444 MPa while the elongation increased to 29% before fracture.

Delamination wear of metal injection moulded 316L stainless steel

The wear behavior of metal injection moulded (MIM) stainless steels was studied using a pin-on-disc apparatus under dry sliding conditions. Pin specimens were MIM 316L stainless steel, while disc specimens were wrought 316L stainless steel. At low sliding speeds (0.2–0.6m/s), the wear rates gradually decreased with increasing sliding speed, but then increased at high sliding speeds (0.6–2m/s). The adhesive-induced delamination wear dominated at low sliding speeds, while abrasive-induced delamination wear dominated at high sliding speeds. At low sliding speeds, the surface densification occurred on the worn surface of pin specimens, hence no difference was found between the wear resistances of MIM pins containing 2% and 6% porosity. In contrast, the abrasive-induced delamination wear at high sliding speeds was enhanced by porosity; therefore the wear rates of MIM pins containing 6% porosity were higher than those of MIM pins containing 2% porosity.

Production of injection moulded 316L stainless steels reinforced with TiC(N) particles

Metal matrix composites, based on 316L stainless steel and reinforced with TiC and TiCN particles, were manufactured following a powder injection moulding route: mixing, preparation of feedstock, moulding, debinding and sintering. The 316L stainless steel and carbide powders were dry mixed and moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for all samples. Binder debinding was performed by solvent and thermal method. After debinding, the samples were sintered at 1250 and 1385°C for 1 h in pure H2. Metallographic studies were conducted to extend densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all samples after wear tests. All powder, fracture surfaces of moulded and sintered samples, and worn surfaces of all the samples, were examined using scanning electron microscope. The sintered density of injection moulded 316L stainless steel samples, reinforced and unreinforced, increases with increasing sintering temperature. The addition of TiC and TiCN improves the hardness and wear resistance with increasing sintering temperature.

Post-sintering thermal treatment of nitrogen containing pressed and sintered and PIM stainless steels

It is known that nitrogen in the sintering atmosphere impairs the corrosion resistance but enhances the strength and hardness of sintered stainless steels. In this study, an additional post-sintering thermal treatment was applied on parts that were sintered in N2 containing atmospheres and its effects on the mechanical properties and corrosion resistance were evaluated. Both pressed and sintered (P/S) 304L and powder injection moulded (PIM) 316L stainless steel compacts were examined. The results show that the Cr2N compound was formed throughout the low density 304L compact, causing poor corrosion resistance when there was nitrogen in the sintering atmosphere. However, the high density PIM 316L compact only contained Cr2N at the surfaces owing to the high sintering temperature and the lack of interconnected pores. This Cr2N compound can be suppressed when the compact is reheated to 1100°C in argon and then cooled at a moderate rate of 57°C min−1. With this post-sintering treatment, even the compact sintered in pure nitrogen showed satisfactory corrosion resistance results, similar to those of hydrogen sintered compacts.

Studies on the Preparation, Characterization and Corrosion Behaviour of Injection Molded 316L Steel Electrochemically Coated by Poly{trans[dichloro (4-vinylpyridine) ruthenium

The present work describes the studies on corrosion of powder injection molded 316L stainless steel potentiostatically coated by poly{trans[RuCl2(vpy)4]} where vpy (4- vinylpyridine) acts as ligand. Scanning Electron Microscopy (SEM) coupled to an Energy Dispersive X-Ray Analysis (EDAX) characterized the coated electrodes. Anodic polarization tests were performed in 3% NaCl to estimate the anodic dissolution current density of the electrode coated by the polymeric material. In addition, the specimens were exposed to salt spray and acid rain simulated environment. The microestrutural analysis indicated that the films were approximately 58 μm thick. Cyclic voltammetry experiments were carried out in 0.1M HTBA/methyl isobutyl ketone solution. The results revealed a scan rate dependent wave corresponding to a Ru2+/Ru3+ redox reaction, thus confirming the presence of ruthenium as metallic center in the polymer backbone. Pitting corrosion was observed in coated specimens only after thirty days of exposure to salt spray and after two days of exposure to acid rain simulated environment.

Solvent debinding kinetics and sintered properties of injection moulded 316L stainless steel powder

A stainless steel (316L) powder having a median particle size of ∼25 μm was injection moulded using binders composed of polyethylene glycols (PEG) and polymethylmethacrylate (PMMA). The PEG content was leached in water and debinding kinetics studied as a function temperature. At 40°C, the removal of PEG was controlled by dissolution of the polymer in water and by diffusion of water and PEG for leaching time <60 min and >60 min, respectively. Water soluble PEG was completely removed within 180 min and the diffusion mechanism controlled the de-binding process at 60 and 80°C. Sintered properties improved with increased sintering temperature and time. The improvement in mechanical properties was less pronounced for a longer soaking time owing to more grain coarsening.

Mechanical properties of metal injection moulded 316L stainless steel using both prealloy and master alloy techniques

Stainless steel 316L MIM components can be made from either prealloyed powders or from master alloys blended with carbonyl iron powder. In this study these two techniques were compared using prealloyed and master alloyed gas atomised powders of − 16 μm and − 22 μm sizes. Four different compounds were prepared, characterised and injection moulded into tensile bars. The bars were compared for green strength, green defects, sintered strength and microstructure. The green components are stronger when carbonyl iron powder is used with the gas atomised master alloy. This material also seems to be less susceptible to moulding defects. The sintering strength of the material produced using the pre-alloyed powder was higher than the master alloyed prepared material. Little difference in mechanical properties existed between the materials fabricated from gas atomised prealloyed − 16 μm and the − 22 μm powders. Also, the viscosity of the mixtures was higher for the − 16 μm material and the master alloy mixtures than for the –22 μm gas atomised prealloyed powders.