Synthesis And Properties Of Fe-Ni Alloy MIM Feedstock Based On Polyaldehyde

Metal powder injection molding(MIM)is a new near net forming technology for spare parts.Binders are the core of this technology.At present,the most common binders are polyaldehyde binders and wax binders.Compared with traditional wax-based feedstock,polyaldehyde feedstock have the advantages of short production cycle,good body shape retention and easy preparation of small and complex shaped parts.At the same time,compared with other magnetic alloys,Fe-Ni alloy has the advantages of small coercivity,high plasticity and excellent rust resistance.In this paper,a new polyaldehyde binder system was developed,and Fe4Ni alloy powder was used to prepare the injection molding feedstock.The effects of binder components and powder loading amount on the rheological properties of feedstock were discussed.The optimal ratio and powder loading amount were determined by comprehensive rheological properties analysis and SEM results.Then,the influence of injection parameters on the quality of blank body was studied and catalytic degreasing was carried out for a batch of standard tensile specimens.Through the properties of sintered products,the quality of the developed polyaldehyde binder system was evaluated,and the effect of heat treatment process on the structure and properties of the body was studied.Finally,the developed Fe4Ni alloy polyaldehyde feedstock was applied to production and good results were obtained.The research results show that:1.According to the comparison and optimization of rheological properties,the optimal powder loading capacity is 58 vol.%and binder ratio is 82%POM+10%HDPE+4%PW+2%MW+2%PEG(wt.%).2.The optimal feedstock P showed the characteristics of pseudoplastic fluid and is uniformly mixed.The non-Newtonian coefficient N value is 0.274 at 195?,the viscosity activation energy E value is 54.084 KJ·mol^-1at shear rate of 500 s^-1,and the rheological index?_STVis 0.0521,which were suitable for injection molding.3.When the injection temperature is 195?,the injection speed is 80 mm/s,and the pressure holding pressure is 70 MPa,the Green part has good formability,uniform composition and no macroscopic defects.4.The catalytic degreasing process was used to remove the binder at 130?,N₂flow rate 80 L/min,oxalic acid flow rate 2.0?4.5 g/min,and degreasing time 12 h.The optimal degreasing rate of the feedstock is 74.6%,91%of the theoretical degreasing rate,which met the production requirements.5.After vacuum sintering at 1290?and Ar+N₂,the sintered billets have uniform microstructure,smooth grain boundary and fewer and even pores.The average density is7.553 g/cm³,which is 96.3%of the theoretical density.The sintering shrinkage rate is15.75%,the average hardness is 26 HRC,and the tensile strength is 415 MPa,which meet the mechanical properties requirements of the product.6.The effects of different tempering temperatures on mechanical properties and microstructure of sintered billets were studied.The results show that after quenching(860?for 20 min,water cooling)+moderate tempering(400?for 1 h,air cooling),the microstructure of the product is uniform and fine,and the mechanical properties of the product are the best.The average hardness and tensile strength of the product are 29 HRC and 590 MPa,respectively.