Materials Science Forum Vols. 534-536

Abstract: The metal injection molding process was applied to produce Ti-6Al-7Nb alloys using 3 types of mixed powders. The first is a mixture of Ti and Al-Nb pre-alloyed powders, the second is a mixture of Ti, Ti-Al alloy and Nb powders, and the third is a mixture of elemental powders of Ti, Al and Nb. The sintered compacts using the first and second powders showed higher density and mechanical properties than the compacts using the third powder which showed many large pores formed due to the dissolution of Al particles during the sintering steps. Eventually, the compacts using a mixture of Ti+Al-Nb or Ti+Ti-Al+Nb powders showed tensile strength of above 800MPa and elongation of above 10%, which are similar to the properties of wrought materials.

Abstract: Gas surface treatment is considered to be especially effective for Titanium because of its high reactivity. In this study, we investigated the gas nitriding mechanism in titanium sintered parts produced by metal powder injection molding (MIM) process. In MIM process, gas nitriding can be surface-treated subsequently after debinding and sintering process. Then, the microstructure and nitrogen content of sintered MIM parts are considered to be greatly influenced by not only nitriding conditions but also sintered conditions. In this study, the effects of sintering time on microstructure such as nitrided layer thickness and hardness was investigated. Focus was given to the effects of specimen size on nitriding process, because the size of micro metal injection molding (μ-MIM) product is so small and the specific surface of that product is so large that the mechanical and functional properties can be subject to change by nitriding.

Abstract: The MIM technology is an alternative process for fabricating near net shape components that usually uses gas atomised powders with small size (< 20 μm) and spherical shape. In this work, the possibility of changing partially or totally spherical powder by an irregular and/or coarse one that is cheaper than the former was investigated. Different bronze 90/10 components were fabricated by mixing three different types of powder: gas atomised spherical powder (usual MIM powder < 22 μm) and two water atomised irregular powders (size < 35 μm and < 140 μm). The blends were made by using only two types of powder in each mixture with the following volume proportions (100/0, 67/33, 33/67, 0/100). The influence of the particle size and shape on the powder packing density and sintering stage was analyzed through the apparent density of the powder blends, as well as, densification, hardness and porosity of the sintered parts. The addition of irregular and/or coarse powder was found to affect the moulding process, although good densifications and hardnesses were obtained in the sintering step. Therefore it could be a promising way to diminish production costs in this technology.

Abstract: The production method of micro sacrificial plastic mold insert metal injection molding, namely μ-SPiMIM process has been proposed to solve specific problems involving the miniaturization of MIM. The sacrificial plastic mold (SP-mold) with fine structures was prepared by injection-molding polymethylmethacrylate (PMMA) into Ni-electroform, which is a typical LIGA (Lithographie-Galvanoformung-Abformung) process. Stainless steel 316L feedstock was injectionmolded into the SP-mold which had micro structures with multi-pillars. The green compact was demolded as one component with the SP-mold, which was decomposed along with binder constituent of feedstock in debinding process. This study focused on the effects of metal particle size and processing conditions on the shrinkage, transcription and surface roughness of sintered parts, which were evaluated by SEM (Scanning Electron Microscope) observation.

Abstract: To overcome the lack of micro manufacturing processes suitable for medium and large scale production as well as to process high resistive materials a special variant of micro injection molding is currently under development: micro powder injection molding (MicroPIM), which already enables the manufacturing of finest detailed components with structure sizes down to a few ten micrometer. In order to expand the scope of application of MicroPIM, tests are being conducted with pure tungsten powders or tungsten alloy powders. As further improvement, micro twocomponent injection molding allows, for example, the fabrication of micro components consisting of two ceramic materials with different physical properties.

Abstract: Mo2FeB2 boride base cermets produced by a novel sintering technique, called reaction boronizing sintering through a liquid phase, have excellent mechanical properties and wear and corrosion-resistances. Hence, the cermets are applied to the injection molding die-casting machine parts and so on. Metal injection molding (MIM) is a suitable processing route for the mass production of complex shaped and high performance components. In general, it is difficult for the liquid phase sintered materials to be applied to the injection molding process because significant shrinkage and deformation occur during sintering. In this study, the MIM process was applied in the production of Mo2FeB2 boride base cermets parts. We investigated that the effect of deoxidization and sintering temperature on mechanical properties and deformation of the cermets. As a result, deoxidization temperature of 1323K and sintering temperature of 1518K were suitable. The MIM products of the cermets showed allowable dimensional accuracy and the same mechanical properties as the press-sintered.

Abstract: This study aims to investigate the effects of hybrid micro/nano powders in a micro metal injection molding (μ-MIM) process. A novel type of mixing-injection molding machine was used to produce tiny specimens (<1mm in size) with high trial efficiency using a small amount of feedstock (<0.05cm3 in volume). Small dumbbell specimens were produced using various feedstocks prepared by changing binder content and fraction of nano-scale Cu powder (130nm in particle size). The effects of adding the fraction of nano-scale Cu powder on the melt viscosity of the feedstock, microstructure, density and tensile strength of sintered parts were discussed.

Abstract: The kneading process and formulations of feedstock obviously affect the quality of MIM products. In the present work, the rheological behaviour of the composite MIM feedstock, metal matrix (Cu) with few additions of ceramic powders (Al2O3), was measured by a selfdesigned/ manufactured simple capillary rheometer. Experimental results show that the distribution between powders and binder is more uniformly when blending time increased. Though high powder loading will increase the feedstock viscosity, the fluidity reveals relatively stable through the load curves of extrusion. Besides, the temperature-dependence of viscosity of the feedstock approximately follows an Arrehnius equation. Basing on Taguchi’s method, the kneading optimization conditions and the rheological model of the feedstock were established, respectively.

Abstract: Two atomized alloy powders, those chemical compositions are Al-10Si-5Fe-1Zr and Al- 10Si-5Fe-4Cu-2Mg-1Zr, were pre-compacted by cold pressing with 350MPa and subsequently hot forged at temperatures ranging from 653K to 845K and at an initial strain rate of 10-2/s in order to produce bulk cylindrical type alloys with the diameter of 10 mm. The addition of Cu and Mg into the present alloy causes a decrease in the eutectic reaction temperature of Al-10Si-5Fe-1Zr alloy from 841K to 786K and results in a decrease of flow stress at the given forging temperature. TEM observation revealed that in addition to Al-Fe based intermetallics, Al2Cu and Al2CuMg intermetallics appeared to display the alloying effect additionally. The volume fraction of intermetallic dispersiods increased by the addition of Cu and Mg. Compressive strength of the present alloys was closely related to the volume fraction of intermetallic dispersoids.

Abstract: In present work, manufacturing technologies of micro parts by micro forging and pressing were studied using strain softening phenomenon in nano grained Al-1.5mass%Mg alloy. During compressive test at 300
, the Al alloy showed stain softening phenomenon by grain boundary sliding regardless of strain rate. Micro spur gear with ten teeth (height of 200 μm and pitch of 250 μm) was fabricated with sound shape by micro forging. During micro forging, increase of applied stress induced by friction between material and die surface was effectively compensated by decrease of stress by strain softening behavior and as a result, flow stress increased only about 50 MPa more than that in compressive test. However, in micro pressing, flow of material did not occurred sufficiently to fill die and the resultant shape of gear was very poor.