The characteristic of molten pool during laser gas nitriding of titanium alloy surface

Poor surface mechanical properties are an important factor restricting the wide applications of titanium alloys, while the laser gas nitriding process can effectively improve the surface mechanical properties. The convection behavior on molten pool surface in the nitriding process was captured using a high-speed camera system, the images of the molten pool surface were processed, the special convection behavior was analyzed, and the convection velocity on the molten pool surface was calculated. The forming characteristics of the nitrided layer section were observed, and the relationship between the special convection behavior of the molten pool and the section forming was analyzed. The experimental results show that the nitriding molten pool convection has the characteristics of discontinuity, locality and randomness; the alternating change of the relationship between the melting point and the temperature of the molten pool leads to the discontinuity of the convection , and the segregation of the molten pool composition and the non-uniformity of the parameters lead to the local and random nature of the convection; the special convection behavior of the nitriding molten pool results in the irregular section of the nitrided layer. According to these characteristics, a scheme of controlling the quality of nitrided layer is put forward by using non-uniform heat source.