Co-sintering of M2/17-4PH Powders for Fabrication of Functional Graded Composite Layers

Stepwise-graded composite layer of M2 tool steel and 17-4PH stainless steel was fabricated by a simple powder layering technique and the isothermal and nonisothermal sintering response of the bilayer were examined. It was shown that the materials exhibit poor compatibility during co-sintering, i.e., the amount of mismatch shrinkage is significant. An improved compatibility was obtained by adding 0.2 wt% B to the stainless steel powder. Formation of relatively dense layer at the bonding zone indicated an enhanced densification rate at the interface. Microstructural studies showed formation of a ferritic interface in M2/17-4PH composite and elongated grains with an intergranular boride phase and martensitic matrix at the bonding zone of M2/17-4PH + B. Increasing the sintering temperature broadened the interface width along with formation of more ferrite and coarser grains at the interface. Mechanical tests indicated higher shear strength and hardness of the interface zone in the composite compared with the individual layers.