Fig.1 Images of a HTP fretting wear system, b schematic diagram of autoclave and fretting test machine, c image of Zr alloy tube and its dimple and d the normal force curves during 300-h test

Fig. 2 3D morphologies and cross-sectional profiles of wear scars on the tubes: a, b 20 N, c, d 30 N, e, f 40 N

Fig. 3 The maximum wear depths and the wear volumes of Zr alloy tube under different normal forces

Fig. 4 Ft − D curves under different normal forces: a1-a6 20 N, b1-b6 30 N, c1-c6 40 N

Fig. 5 Variation of friction coefficients with test time under different normal forces

Fig. 6 Variation of a single dissipated energy and b the wear coefficients of Zr alloy tubes under different normal forces

Fig. 7 SEM images of wear scars on Zr alloy tube under different normal forces: a, b 20 N, c, d 30 N, e, f 40 N

Fig. 8 SEM morphologies with higher magnification of the wear scars on Zr alloy tube under different normal forces: a, b 20 N, c, d 30 N, e, f 40 N

Fig. 9 Cross-sectional morphologies of worn area on Zr alloy tube under 20 N: a overall backscatter electron (BSE) image; b magnified image of worn area; c magnified image of delamination region; d magnified image of unworn area

Fig. 10 Cross-sectional morphologies of worn area on Zr alloy tube under 40 N: a overall BSE image; b magnified image of worn area; c magnified image of region A; d magnified image of region B

Fig. 11 Micro-XRD patterns of worn areas under different normal forces

Fig. 12 Raman spectrum of worn areas under different normal forces

Fig. 13 Simplified delamination process and the corresponding images of seven phases