简介概要

Influence of surface finish and annealing treatment on oxidation behavior of Ti-48Al-8Cr-2Ag alloy

来源期刊:中南大学学报(英文版)2009年第4期

论文作者:席艳君 刘泳俊

文章页码:541 - 546

Key words:Ti-48Al-8Cr-2Ag alloy; coating; surface finish; annealing; oxidation behavior

Abstract: The effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy was investigated at 900 and 1 000 ℃, respectively in air. Thermal gravimetric analysis (TGA) was conducted for the characterization of oxidation kinetics. The microstructures of oxide scales were studied by scanning electron microscopy (SEM) and transmission election microscopy (TEM) techniques. Unfavorable effect of the annealing treatment on the oxidation behavior of the coating was also investigated. The results indicate that the oxidation behavior of the alloy is influenced by surface finish and annealing treatment. The oxidation rate of ground sample is lower than that of the polished alloy at 1 000 ℃ in air. The former forms a scale of merely Al2O3, and the latter forms a scale of the mixture of Al2O3 and TiO2. Annealing can improve the formation of TiO2.

基金信息:the Science and Technique Foundation of Henan Educational Committee, China



详情信息展示

J. Cent. South Univ. Technol. (2009) 16: 0541-0545

DOI: 10.1007/s11771-009-0090-7

Influence of surface finish and annealing treatment on

oxidation behavior of Ti-48Al-8Cr-2Ag alloy

XI Yan-jun(席艳君), LIU Yong-jun(刘泳俊)

(School of Materials and Chemical Engineering, Zhongyuan University of Technology, Zhengzhou 450007, China)

                                                                                                

Abstract: The effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy was investigated at 900 and 1 000 ℃, respectively in air. Thermal gravimetric analysis (TGA) was conducted for the characterization of oxidation kinetics. The microstructures of oxide scales were studied by scanning electron microscopy (SEM) and transmission election microscopy (TEM) techniques. Unfavorable effect of the annealing treatment on the oxidation behavior of the coating was also investigated. The results indicate that the oxidation behavior of the alloy is influenced by surface finish and annealing treatment. The oxidation rate of ground sample is lower than that of the polished alloy at 1 000 ℃ in air. The former forms a scale of merely Al2O3, and the latter forms a scale of the mixture of Al2O3 and TiO2. Annealing can improve the formation of TiO2.

 

Key words: Ti-48Al-8Cr-2Ag alloy; coating; surface finish; annealing; oxidation behavior

                                                                                                            


1 Introduction

Conventional TiAl alloys do not form protective oxide scales during high temperature exposure [1-5]. TiAl-base intermetallics have received more attention as potential high temperature structural materials because they have many properties beneficial to high temperature applications, including low density, good high temperature strength, and high stiffness. In order to enhance the oxidation resistance of TiAl-base intermetallics, several kinds of coating have been investigated [6-9]. Recently, some promising results have been found in the Ti-Al-Cr system [10-16]. However, there have been few reports concerning the influence of surface finish and annealing treatment on the oxidation behavior of TiAl alloy.

Among coating processes, magnetron sputtering is a very suitable method to manufacture thin films with complex and homogeneous chemical composition as well as uniform morphology and coating thickness. The deposition process runs in a vacuum chamber refilled with high purity argon. When no external heating is used during the coating deposition, substrate temperatures are comparatively low due to impinging species and argon ions as well as latent heat of condensation. Therefore, the microstructure change of the substrate alloy can be avoided during deposition, which is sometimes a problem for plasma spraying and evaporation techniques on heat sensitive materials [17].

Some researchers studied the oxidation of TiAl alloy and its coating [4-5, 8, 12], but few investigated the influence of the surface treatment on the oxidation behavior. In this work, a microcrystalline TiAl coating was deposited on the surface of the same substrate by magnetron sputtering. The oxidation behavior of TiAl alloy and its coating was investigated. Special emphasis was placed on a detailed examination of the effect of surface finish and annealing treatment on the oxidation behavior of Ti-48Al-8Cr-2Ag (molar fraction, %) alloy and coating at 900 and 1 000 ℃ in air.

2 Experimental

The nominal composition of the alloy was Ti-48Al-8Cr-2Ag. The resulting microstructure was γ-TiAl and Laves phase [12]. The Ti-48Al-8Cr-2Ag coating was prepared by magnetron sputtering technique. The target and the specimens, with dimensions of    380 mm×126 mm×7 mm and 10.0 mm×10.0 mm×2.5 mm respectively, were cut from an alloy ingot. The specimens were ground 600-grit SiC paper, peened and ultrasonically cleaned in ethanol. The peening treatment was performed to improve the adhesive energy. The morphology and microstructure of the coating were narrated in detail elsewhere [12]. The sputtering parameters were as follows: the pressure of reaction chamber, 0.5×10-2 Pa; argon pressure, 0.2-0.3 Pa; substrate temperature, 200 ℃; power, 1 800 W; and sputtering time, 8 h. The chemical composition of the

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