PSI - Issue 5

Hirotaka Tanabe et al. / Procedia Structural Integrity 5 (2017) 1005–1010 H Tanabe et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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3. Experimental results and discussions

Thrust type rolling contact fatigue tests were carried out for CrAlN coated specimens laser-quenched under various laser power P , and their delamination initiation lives were investigated. Figure 5 shows the examples of delamination of CrAlN coating initiated by rolling contact fatigue test. Figure 6 shows the relationship between the delamination initiation life and laser power. From P = 800W to 880W, the delamination initiation life was increased with laser power. However, the delamination initiation life under P = 900W was shorter than P = 880W. It was found that the laser quenching after coating had the effect to improve the delamination initiation life of CrAlN coated specimen, however the excessive laser power decreased the delamination initiation life. In order to investigate the reason for the variation of delamination initiation life, the adhesive strength and the hardness of laser irradiated CrAlN coatings were investigated. The adhesive strength of these coatings was measured using a scratch tester (CSR-01, Resca Co. Ltd., Japan). The hardness was measured using a nano-indentation tester (ENT-1100a, Elionix, Japan). The indentation depth was fixed at 0.25  m, corresponding to 1/10th of the film thickness, to avoid including the influence of substrate hardness. Figure 7 shows the measurement results of the adhesive strength and the hardness of laser irradiated CrAlN coating. The adhesive strength increased with increasing the laser power from P = 800W to 880W, and decreased at 900W. Hardness was almost constant from P = 800W to 880W and then decreased at 900W. From these results, it was considered that the increase of delamination initiation life from P = 800 to 880 W could be explained by the improvement of the adhesive strength derived by the laser quenching after coating, and the decrease of the delamination initiation life under the excessive laser power condition was caused by the decreases of the adhesive strength and/or the film hardness.

a

b

c

Fig.5 Delaminations of CrAlN coating initiated by rolling contact fatigue test

7 ; (b) P = 880W, N

8 ; (c) P = 900W, N

(a) P = 840W, N i = 5.23×10

i = 1.86×10

i = 2.14×10 7

0.5 1.0 1.5 2.0 2.5

8 ]

N i [ × 10

780 800 820 840 860 880 900 920 0

Delamination initiation life

Laser power, P W

Fig.6 Relationship between delamination initiation life of CrAlN coating and laser power