Studies On The Formation Of Iron-based Metal Powders Via Selective Laser Sintering Combined With Isostatic Pressing

Indirect Selective Laser Sintering (SLS) can manufacture any types of parts with complex structure, but with high porosity and low strength. The above shortages could be improved, by using the technology of vacuum sintering and infiltrating, however, the problem of deformation retraction easily happened in sintered parts, and mechanical properties were"polluted"by infiltration materials. Therefore, it will be a combination formed SLS/Isostatic Pressing (IP) complex process to achieve high performance and complicated parts, which can utilize fully their own specific advantages. Main research contents and conclusions are below.(1) Composite process of SLS/Cold Isostatic Pressing (CIP)/Hot Isostatic Pressing (HIP) was developed. Iron alloy system composite powders composed of alloy element powders, such as Fe-C,Fe-Ni-C and Fe-Cu-C, and AISI304 stainless steel powders, were developed with epoxy resin E-12 as binder material. Alloy parts made by the new process obtained high density and good mechanical properties without shape error through SLS, degreasing, CIP, high-temperature sintering and HIP.(2) Canning materials used in SLS/CIP are investigated. Complicated SLS parts could be sealed by silicon rubber RTV-2 which has high curing-process rate, high elasticity and good performance of tightness. RTV-2 is suitable for SLS/CIP canning material.(3) Density of parts after each step of the process were measured according to the Archimedes principle, The results showed that density was about 40% after degreasing, and could be 90% after CIP. Through vacuum sintering and HIP, density increases continually. And the best one was Fe-0.5C parts with density of 98.5%.(4)Relation between density and CIP working pressure of AISI304 stainless steel was researched, and the result approximately met the log-log pressing theory.(5)Mechanisms and technologies of SLS/CIP, high temperature sintering and HIP are investigated with effects of their technology parameters. Microstructures, mechanical properties of the mentioned alloys were tested respectively via environmental scanning electron microscope, universal testing machine. Microscopic structure of Fe-C alloy is granular pearlite and ferrite. According to different components, there were Fe-Ni,Fe-Cu composition in Fe-Ni-C and Fe-Cu-C alloys respectively. Mechanical properties were better than infiltrating parts. And the best one was Fe-5Cu-0.5C alloy with the property: yield strength-417MPa, tensilestrength-521MPa, Yang's modulus-139.5GPa, elongation-7.9%.In conclusion, the complex process of SLS/CIP/HIP is feasible to manufacture metal parts with high density, good mechanical property and complex structure. This work further developed SLS technology in the direction of high efficiency manufacturing metal parts with high complex structure and fine property. Hence the work provides a good contribution to the application of indirect SLS and IP both theoretically and practically.