Surface Modification of TC4 Alloy with Pack Cementation Yttria-Doped Aluminide Coatings:An Experimental Study

The surfaces of TC4 alloy,an advanced aerospace material,were modified with yttria-doped aluminide coatings,synthesized by pack cementation with the agent of 15 Al-2 Y₂O₃-6 NH₄Cl-71 Al₂O₃(wt%) for oxidation-resistance enhancement.The influence of the yttria-doping on the microstructures,phase-structures and oxidation resistance was investigated with X-ray diffraction,scanning electron microscopy and energy dispersive spectroscopy.The results show that the yttria-doping had a major impact.To be specific,the yttria-doping significantly reduced the residual stress,increased the interfacial adhesion and inhibited crack formation.Al₃Ti phase dominated the modified surfaces,and small amounts of Al₂₃V_6,Al₂Ti₍3 )and Al₂Ti phases were correlated to a synthesis temperature of 900℃,940℃ and 980℃,respectively.Oxidized at 1,000℃ for 50 h,the compact Al₂O₃-coatings formed,on the TC4 alloy modified at 940℃ for 2 h,and considerably enhanced the oxidation resistance of TC4 alloy.