Microstructure and mechanical properties of WC-Co-based cemented carbide with bimodal WC grain size distribution

In order to improve the wear resistance of coarse-grained WC-Co cemented carbides,the fine WC powder were used to reinforce the metallic binder.These WC-Co-based cemented carbides having bimodal WC grain size distributions were synthesized by liquid phase sintering.For comparison,the cemented carbides having unimodal WC grain size distributions were synthesized.The microstructure,hardness,fracture toughness and wear resistance of these cemented carbides were investigated.The results show that adding fine WC powder is an effective method to improve the wear resistance of coarsegrained WC-Co cemented carbides.The WC size,mean free path and fracture toughness decrease with the addition of fine WC powder,while the hardness exhibits an opposite trend.The impact-wear coefficient of bimodal distribution cemented carbides is noticeably lower than that of the unimodal one with the same hardness,which means that the cemented carbides with bimodal grain structure have better combination of hardness and impact-abrasive wear resistance.The impact-abrasive wear mechanism of the bimodal cemented carbides is that the fine WC grains prevent abrasive wear and the coarse WC grains prevent impact wear.

Corrosion behavior of additive-manufactured NiFeCrMo alloys in various corrosion media

To understand the corrosion performance of additive-manufactured Ni-based in various corrosion media during the actual engineering application environment,the corrosion properties of NiFeCrMo alloys were investigated in 3.5 wt.%NaCl solution,1 mol/L H2SO_(4) solution,and 1 mol/L KOH solution,using potentiodynamic polarization and electrochemical impedance spectroscopy.The electrochemical measurement results revealed that the additive-manufactured NiFeCrMo alloys have higher corrosion resistance in all three solutions,compared with the as-cast samples.The results of the scanning electron microscope confirmed that the degree of additive-manufactured NiFeCrMo alloys after potentiostatic polarization in all three solutions is less serious.X-ray photoelectron spectroscopy analysis revealed that the enhancement of the corrosion resistance for the additive-manufactured NiFeCrMo alloys is attributed to the modification of the composition of the passive films.Additive manufactured processing promotes the enrichment of the element of Cr or Mo in the passive film and it suppresses the formation of the oxidation of the element of Fe,leading to higher stability of the passive films.The reason for the higher corrosion resistance of the additive-manufactured NiFeCrMo alloys was related to the enrichment of the element of Cr,as well as the lower content of the elements of Ni and Fe near the grain boundaries,which are beneficial to forming a more compact passive film.The combined results are essential for the applications of high-strength Ni-based as structural materials in a corrosion environment.