Cavitation erosion resistant coating of NiTi made by laser plasma hybrid spraying

Abstract

Titanium alloys are light and have high corrosion resistance, but they have low wear resistance. This study was aimed to make erosion resistive coating on titanium base metal by the laser/plasma hybrid spraying method. NiTi intermetallic compound is known as a high cavitation erosion resistant material. In this work, NiTi intermetallic compound coating was formed directly from the simply mixed powder of Ni and Ti. This laser/plasma hybrid spraying system was constructed with 5kW CO2 laser and low pressure DC plasma spraying unit In this system, the every coated layer by plasma spraying was remelted and rapidly solidified by the CO2 laser irradiation. So, it is possible to synthesize intermetallic compound coating from the simply mixed powders.The major results are as follows: 1) Erosion resistance of the coating highly depended on laser irradiation condition and the Ni/Ti mixed ratio. The highest resistance was obtained in combinations with irradiation power density of more than 60 kW/cm2 and with the Ni/Ti atomic ratio of 55/45. The test result on the cavitation erosion resistance showed 380 times higher than that of Ti6Al4V alloy. 2) Following factors were important to increase the cavitation erosion resistance. i) The coating consisted of austenitic NiTi phase without martensitic NiTi phase as well as no other intermetallic compound, such as NiTi2, Ni3Ti etc. ii) The austenitic NiTi phase contained excess soluble Ni by rapid cooling, which caused high work hardening property. Titanium alloys are light and have high corrosion resistance, but they have low wear resistance. This study was aimed to make erosion resistive coating on titanium base metal by the laser/plasma hybrid spraying method. NiTi intermetallic compound is known as a high cavitation erosion resistant material. In this work, NiTi intermetallic compound coating was formed directly from the simply mixed powder of Ni and Ti. This laser/plasma hybrid spraying system was constructed with 5kW CO2 laser and low pressure DC plasma spraying unit In this system, the every coated layer by plasma spraying was remelted and rapidly solidified by the CO2 laser irradiation. So, it is possible to synthesize intermetallic compound coating from the simply mixed powders.The major results are as follows: 1) Erosion resistance of the coating highly depended on laser irradiation condition and the Ni/Ti mixed ratio. The highest resistance was obtained in combinations with irradiation power density of more than 60 kW/cm2 and with the Ni...