材料期刊网

以TiB2粉末和Ni+TiB2粉末混合物分别作为预置层,采用激光原位技术在钛合金表面制备出2类复合涂层.运用XRD,SEM,EPMA与硬度计等实验手段,对合成的复合涂层进行测试分析.结果表明,Ni添加之前,可获得TiB2颗粒与TiB短纤维增强钛基复合涂层,但涂层表面成型质量较差.Ni添加之后,既可改善涂层的表面成型质量,又可生成bcc结构的NiTi合金填充在TiB2颗粒与TiB短纤维周围.Ni的添加还可使TiB2颗粒得以细化,且涂层中出现了β-Ti基.Ni的添加使涂层的显微硬度值降低,但涂层的断裂韧性得以提高.钛基复合涂层主要通过颗粒脱粘与短纤维断裂偏移方式使裂纹发生偏转来提高涂层的断裂韧性.

Titanium alloys have been known as useful materials for their superior mechanical properties,low density and high specific strength.However,the application of conventional titanium alloys on engine parts of airplane is limited by their poor wear resistance,low fatigue strength and low hardness.Particles reinforced titanium matrix composites have attracted extensive investigation in material science and engineering.Mechanical properties can be improved by reinforcing the loaded outer layer of Ti with ceramic particles.TiB and TiB2 are considered as the excellent ceramic reinforced particles for their compatible physical and thermodynamic properties,high hardness and Young's modulus of elasticity.However,TiB2 has high brittleness.The intermetallic compound NiTi,wellknown for its shape memory effect and pseudo-elasticity,is one of the rarely few intermetallic compounds having excellent combination of high strength,ductility and toughness as well as excellent wear resistance and fabrication processing properties.An in situ TiB/TiB2 structured ceramic materials as the reinforcing phase and NiTi interrnetallic phase as the matrix would be expected to have an outstanding combination of high hardness and toughness.To investigate the microstructure and properties of the cladded layers,two types of composites were prepared by laser cladding powders containing TiB2 and Ni+TiB2 as a preset level on the surface of titanium alloy.The composite coatings were analyzed by XRD,SEM,EPMA,micro hardness tester and brinell hardness.The results showed that TiB2 particulate and TiB short fiber reinforced titanium matrix composite coating were obtained,which had poor quality of coating shape when Ni was not added.The coating was mainly composed of TiB2,TiB,Ti and NiTi phase when Ni was added and surface coating quality was improved and the bcc structure of NiTi alloy was filled with TiB2 particulate and TiB short fiber surrounding.The coating was coarse with particle size of TiB2 at 3～5 μm when Ni was not added,while it contained fine particles of TiB2 with particle size of 0.5～3 μm and β-Ti base appeared when Ni was added.The micro-hardness of the coating was reduced when Ni was added,but the fracture toughness of the coating increased.The mechanism of toughening was discussed based on fracture behaviors.Fracture toughness of titanium matrix composite coatings were improved mainly through particle debonding and short fiber breakage by the offset resulting in crack deflection.