Titanium cermets were successfully synthesized on the surface of biomedical grade titanium alloys by using sequential carburization method. The mechanical properties such as hardness, fracture toughness and plasticity were measured to estimate the potential application of titanium cermets. The results show that after carburization the surface hardness of titanium cermets was 778 HV, with a significant improvement of 128% compared with that of titanium alloys. In addition, the fracture toughness of titanium cermets was 21.5 × 10^6 Pa.m^1/2, much higher than that of other ceramics. Furthermore, the analysis of the loading-unloading curve in the nanoindentation test also indicates that the plasticity of titanium cermet reached 32.1%, a relatively high value which illustrates the combination of the metal and ceramics properties. The results suggest that sequential carburization should be an efficient way to produce titanium cermets with hard surface, high toughness and plasticity.
Reliability and wear resistance of cutting picks play a significant role in coal mine exploitation with coal shearers.Tool bit separation,blade breaking,severe erosion of the cutting body and fatigue fractures are the main reasons for failure of cutting picks.We carried out carburization on a 30CrMnMo alloy to synthesize a new cutting pick material with improved mechanical properties and high wear resistance.The results indicated that carburization can effectively strengthen the surface of the 30CrMnMo alloy by forming a thick carburized layer and thus significantly improve the surface hardness and wear resistance.In addition,the excellent toughness of 30CrMnMo alloy as a substrate of cutting picks can prevent brittle ruptures and fatigue fractures under high impact stress conditions.The significant decrease in both frictional coefficient and rate of erosion of this carburized 30CrMnMo alloy suggests that this alloy is a potential material for cutting picks of coal shearers after rational carburization.
LUO YongZHANG DekunWANG QingliangLIU HongtaoCHENG GangGE Shirong
Medical forged CoCrMo alloy was treated by plasma nitriding process.The microstructures were characterized by 3Dprofiler,SEM and XRD.The tribological properties were investigated under lubrication of 25% bovine serum solution.Resultsshow that plasma nitriding is a promising process to produce thick,hard,and more wear resistant layers on the surface of CoCrMoalloy.All nitrided samples showed an important increase in the surface hardness due to the formation of harder CrN andCrN phases with compact nano-crystalline structures.The typical hardness values of HVincreased almost two times thanuntreated one.Under bovine serum lubrication,at low nitriding temperature the Coefficient of Friction (COF) of nitrided samplewas lower than that of untreated sample,but at high nitriding temperature the COF was almost the same as the untreated one.Compared with the untreated sample,the nitrided samples showed lower wear rates and higher wear resistance under differentnitriding temperatures.The adhesive wear is the main mechanism for untreated CoCrMo alloy and the wear mechanisms ofnitrided ones are the fatigue wear and slight adhesive wear.It is concluded that the improvement of wear resistance is ascribed tothe hard nitride formation of CrN and CrN phases at the nitrided surfaces.
Qingliang Wang,Lei Zhang,Jiandong Dong School of Material Science and Engineering,China University of Mining & Technology,Xuzhou 221116,P.R.China
