Surface Modification Of 17-4PH Stainless Steel Powders And Injection Molding Feed

Metal Powder Injection Molding(MIM)is a near-net forming method suitable for the production of complex shape products with high precision and high production efficiency.The key to the technology of MIM is to improve the powder loading,the strength of the green body and the fluidity of the feed,as well as the strength and precision of the product.The prior art tends to focus on metal powder properties,binder properties,component ratios,etc.,but rarely involves the surface state of the metal powder and its interaction with the binder,which have important influence on MIM.In this paper,silane coupling agent is used to modify 17-4PH stainless steel powder to enhance the interaction between stainless steel powders and binder.The main research contents are as follows:(1)3-aminopropyltriethoxysilane(KH550),3-glycidyloxypropyltrimethoxysilane(KH560),propyltrimethoxysilane(N313),trimethoxyoctylsilane(N318), dodecyltrimethoxysilane(N3112)and cetyltrimethoxysilane(N3116)were used to surface modify 17-4PH stainless steel powders,respectively.XPS,TG,particle size analysis,zeta potential,and sedimentation volume were used to characterize the surface modification effect of stainless steel powders.The coupling agent was chemically linked to the 17-4PH stainless steel powder surface.The zeta potential of the modified stainless steel powder changed significantly,and the sedimentation volume decreased significantly.(2)For high-density polyethylene/high-density polyethylene wax(PE/PW)binder system,the effects of surface modification on feed fluidity,critical powder loading,as well as strength,hardness,density and cross-section of green body were investigated.It was found that the fluidity of the long-chain alkyl silane coupling agent modified stainless steel powder feed was increased compared with the unmodified 17-4PH feed,and the critical powder loading was increased by 2 vol%.For the amino and epoxy silane coupling agent modified stainless steel powders,the interaction between the powder and the binder is enhanced,and the powder is uniformly dispersed;the flexural modulus,hardness,and density of the corresponding green body are increased.(3)For polyoxymethylene/high density polyethylene wax/stearic acid(POM/PW/SA)binder system,the critical powder loading of the amino and epoxy silane coupling agent modified stainless steel powder feed reached 61 vol%and 62 vol%,respectively,which was increased by 1 vol%and 2 vol%compared with the unmodified feed.The SEM results show that the powders modified by amino group and epoxy silane coupling agent are uniformly dispersed,the powder and binder are well combined,and the combination of alkyl modified and unmodified powder and binder is poor.The flexural modulus of the epoxy and amino modified bodies reached 3708 MPa and 2122 MPa,respectively,which was higher than that of the unmodified and the alkyl modified body.The epoxy-modified body has a density of 5.03 g/cm~3 and a degreasing rate of 99.83%,which is higher than other samples.After degreasing and sintering,the epoxy modified sample has the smallest diameter expansion rate and shrinkage in the longitudinal direction.Compared with the unmodified and other modified powder samples,the epoxy silane coupling agent modified 17-4PH stainless steel powder has a good effect.