Research On Preparation And Tribological Properties Of Cr-Al Alloyed Layer On TC21 Modified By Double Glow Plasma Surface Alloying

TC21 titanium alloy is a new kind of ?+? two-phase titanium alloy with excellent damage tolerance properties, which has high tensile strength, fatigue strength, high toughness, good crack propagation resistance and good welding performance. In the field of aeronautics and astronautics, it has great application prospect. But some disadvantages limit its further application in aerospace components. It should be due to the low surface hardness, poor tribology. To solve these problems, the Cr-Al alloyed layer were prepared TC21 alloy surface using the doubleglow plasma surface alloying?DGP?technology.The optimum process parameters of Cr-Al alloyed layer were listed as follows: source voltage: 1000 V, cathode voltage: 450 V, air pressure: 40 Pa, holding time: 4h. SEM was used to the detected the morphology of the Cr-Al alloyed layer, EDS was used to detect the element distribution and XRD was used to identify the phase. It turns out that Cr-Al alloyed layer with thickness 35?m was compact and homogeneous. The mainly surface phase structure is A1₈Cr₅?Al₇Cr?Al₁₁Cr₄?Cr?Al₉Cr₄ and Cr2 Ti. The hardness of Cr-Al alloying layer was 946 HV0.1, which was about three times more than the substrate. The scratch tests showed that the bond between TC21 alloy and Cr-Al alloyed layer was excellent and the layer at least could withstand 71 N vertical load The hardness and elastic modulus of the Cr-Al alloy layer were 7.506 GPa and 555.43 GPa, which were 2.36 and 3.65 times larger than those of the TC21 substrate, respectively.Wear tests under different process parameters indicated that the friction coefficient, wear volume, the wear scar width and depth of the Cr-Al alloyed layer were much lower than TC21 substrate. The tribological properties were improved. When the sliding speed increased from?5m/min and 10m/min? to high speed?15m/min and 20m/min?, the wear mechanisms of the Cr-Al alloy layer transformed from slight scratch to oxidation wear and delamination wear. Light spalling of the Cr-Al alloyed layer occurs under 730 g load. Dense oxide film was constantly generated to protect its surface at 500°C, and the oxide film was continuously failure. The friction and wear properties of the layer and TC21 alloy were the worst when the friction pair was Si3N4.