Microstructure and Wear Resistance of Cr-Al-Y Co-Deposition Coatings on TiAlNb9 Alloy

The work aims to improve wear resistance of TiAlNb9 alloy. In this paper, Y modified Cr-Al coating was prepared on TiAlNb9 surface and diffusing and co-penetrating Cr-Al-Y for 2 h under 1 050 ℃. The coating was prepared in a vacuum furnace. The infiltration agent included high purity Cr powder, Al powder and Y₂O₃ powder. NH₄Cl was used as catalyst and Al₂O₃ was used as filler. German Zeiss SIGMA 500 scanning electron microscope (SEM) and its own energy spectrum analysis equipment (EDS) were used to observe and analyze the surface, cross-section microstructure and element distribution of the Cr-Al-Yco-deposition coating. The phase composition of the Cr-Al-Y co-deposition coating was analyzed by XRD-6000 X-ray diffractometer (XRD). The friction properties of the TiAlNb9 alloy and the Cr-Al-Y coating were compared. The results showed that all Cr-Al-Y coatings prepared with different contents of Y₂O₃ were provided with a multi-layer composite structure. Thickness of the Cr-Al-Y coatings firstly increased and then decreased with the addition of Y element in the pack. The thickness of 2Y coating was the largest. The outer layer of 0Y coating was Ti₄Cr and (Ti, Nb)Cr₄ phases. The outer layers of the 2Y and 4Y coatings prepared at 1 050 ℃ for 2 h were mainly composed of TiCr₂, TiCr, Ti₄Cr and (Ti, Nb)Cr₄ phase. The inner layers of all the coatings were mainly composed of Ti₂Al phase, and the Interdiffusion zone were mainly composed of Nb-rich γ-TiAl phase. At room temperature, the hardness test showed that the microhardness of Cr-Al-Y coating decreased gradually from the outer layer to the inner layer, and was higher than that of TiAlNb9 alloy. The microhardness of the Cr-Al-Y coating was up to 1 567.3HV9.8, which was about 4 times of the surface hardness of TiAlNb9 alloy. The friction and wear test was carried out by WTM-2E controllable atmosphere micro friction and wear tester. The friction material was GCr15 ball (diameter 4 mm, hardness 740HV), the load was 5 N, the friction radius was 2 mm, the constant speed was 224 r/min, and the friction time was 60 min. Before and after the experiment, the samples were weighed by FA1004 high-precision electronic analytical balance (0.1 mg). The wear scar morphology was analyzed and characterized. The friction coefficient of TiAlNb9 alloy was about 0.7 and fluctuates greatly. The friction coefficient of Cr-Al-Y coating was stable at about 0.37, and the fluctuation range was very small. The wear rate of Cr-Al-Y coating against GCr15 ball was much lower than that of TiAlNb9 alloy. The friction and wear tests showed that the friction coefficient and wear rate of the Cr-Al-Y coating were lower than those of TiAlNb9 alloy at room temperature when it rubs against GCr15 ball, showing excellent wear resistance. Severe plastic deformation occurred on the surface of TiAlNb9 alloy after friction with GCr15 ball, and a large number of fine scratches and abrasive particles were distributed in the wear zone. The wear mechanisms of TiAlNb9 alloy were ploughing wear, abrasion wear and adhesive wear. There was no plastic deformation on the surface of GCr15 ball after rubbing with Cr-Al-Y coating, and small scratches and adhesions were distributed in the wear area. The wear mechanisms of the Cr-Al-Y coating were delamination abrasion wear and grain-abrasion wear. The experimental results showed that the co-permeation layer prepared when the Y₂O₃ content in the infiltration agent was 2% had the best effect. The Cr-Al-Y co-deposition coating could effectively improve the friction and wear resistance of TiAlNb9 alloy.