There are many advantages in nitriding process, but the formation of white layer sometimes results in trouble. The formation of white layer can be reduced by controlling the nitriding atmosphere appropriately. In this experiment, the nitriding atmosphere is prepared by mixing NH3 and H2. An oxygen sensor is used to detect the condition of the atmosphere, and the value of output voltage (EMF) is used as a signal for controlling the flow rate of H2. The experimental results show that the thickness of white layer can be reduced effectively by controlling the flow rate of H2 through the voltage reading of the atmosphere. Meanwhile, the hardness and the depth of nitriding layer could still be maintained. For nitriding at 550 °C, no white layer is formed when EMF is controlled above 1160 mV and a satisfying hardness distribution of the nitriding layer can be obtained when EMF is controlled at 1140 mV.
This work focused on the wear performance of the clad layers which were formed with cladding titanium nitrides (TiN) powder on the JIS SKD11 tool steel by the gas tungsten arc welding (GTAW) method. A rotating type tribometer was used to evaluate the wear behavior of the clad specimens under different sliding conditions. Furthermore, a nanoindenter was used to measure the hardness and elastic modulus of the reinforcements. According to the wear test results, the wear performance of the specimens cladded with TiN powder was better than that of the JIS SKD11 tool steel specimens. During dry sliding wear test, the clad layers exhibited a strong wear resistance because they contained the hard TiN reinforcements. Therefore, the wear performance of the clad layers was substantially better than that of the SKD11 specimens under all the test conditions in this study. In addition, produced oxide films might influence the wear behavior of different specimens during the wear testing, and oxidation wear would even dominate the wear behavior of the clad layers under some conditions.
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