Microstructure And Property Research Of Titanium And Titanium Alloy Surface Modified Coating Base On Electrospark Deposition

Titanium alloy have any advantage such as small density, high specific strength, superior heat resistance, excellent fatigue endurance and pleasurable croop property, play a crucial role in aviation, spaceflight, navigation, energy and chemical industry, automobile, metallurgy and nuclear industry. Titanium and titanium alloy have low hardness, high friction coefficient, poor abrasion resistance, lively nature, restrict its application. The electrospark deposition technology, for the surface modification of titanium and titanium alloy, can improve its surface property.The NiCr, CoCr, WC modified coating were prepared on substrate of TA2 by DZ-4000 III electrospark deposition/surfacing welding machine, its organization, performance and combining mechanism were inspected. The research shows that, the quality of modified coating decreases significantly, defects such as cracks in modified coating surface and interior increase with the rising of deposition voltage; the thickness of modified coating can’t always increase with the growing of deposition time; the main elements between the modified coating and substrate diffuse. CoCr modified coating has poorer quality and more surface faultiness relative to the Ni Cr, WC modified coating. The microhardness of WC modified coating is up to 950.7HV200 g, CoCr modified coating takes second place, NiCr modified coating last; with the increase of distance to the modified coating surface, its microhardness gradually reduces; the microhardness change trend shows that the transition zone exists between the coating and substrate. Due to the lower thickness(about25μm)and poorer fusion with the substrate of WC coating, its application is greatly limited. Consequently, prepared Zr/WC composite modified coating(adopting Zr as middle tier), its microhardness can reach 960.5HV200 g, its thickness is about 50μm. Explored Zr Ti coating on TC11 alloy, the thickness of coating can reach 200 μm, the microhardness of modified coating is over 700HV200g; the main elements between the modified coating and substrate diffuse, tightly combined with substrate,blowhole can be found in modified coating inside without micro cracks,the TC11 alloy surface is modified. Microscopic analysis shows that, it’s metallurgy combination between the coating and the substrate.Modified layer itself has pleasurable strength, the intensity of NiCr coating is up to 500 MPa, the intensity of CoCr coating is up to 350 MPa. Residual stress distribution of the modified coating is inhomogeneous, both tensile stress and compressive stress exist. The residual compressive stress can improve the fatigue strength of modified coating, inhibit the generation of fatigue crack and reduce the fatigue crack propagation rate by increasing the crack closure effect.The discharge mechanism of electrospark deposition is contact discharge. Using high speed photography observed the electrospark deposition arc starting until the formation of the whole process of spraying. The loss of the electrode material exists in the process of electrospark deposition, increases as the voltage, deposition rate of electrode to substrate educes.