Specific wear rates were calculated from a series of micro-scale abrasive tests by means of the calotte-grinding method. The tested material was a CrN coating deposited by arc evaporation on ionnitrided AISI H13 steel. Characterizations included: phase analysis, chemical composition, metallography, microhardness, micro-scratch resistance and nano-indentation hardness. On wear testing, the counter body was a 30 mm diameter steel ball rotating at a tangential speed of 9.42 m/min and normal load of 0.54 N. The abrasive was a mono-crystalline diamond micro abrasive paste, 1 micrometer grit. Wear volumes were calculated by measuring the wear scars at various test intervals. In non-perforating tests, Archard's wear equation was directly employed for calculating coating wear rate as the slope of the linear least square data fit. In perforating tests, Allsopp's method was employed for the simultaneous determination of coating and substrate wear rates, from the slope and intercept values of the linear least square data fit. Coating specific wear rate values obtained from both non-perforating and perforating tests were very consistent, with a relative difference within 6%. Relative errors in specific wear rate values were estimated to be of the order of 0.05 for the coating and 0.2 for the substrate.

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A laboratory-scale thermal fatigue simulator has been designed, constructed, and commissioned by the authors for studying thermal fatigue of hot-working tool steels by means of rapid alternated heating and cooling. The basic design features, construction characteristics, and test capabilities of the thermal fatigue simulator are presented in this paper. Thermal fatigue simulations were run on hardened and tempered AISI H13 hot-working tool steel specimens in time-control with heating and cooling times of 15 and 10 s, respectively, and a total number of 500 and 2000 thermal fatigue cycles. The experimental results have demonstrated that the simulator is capable of producing thermal fatigue cracks with the same characteristics of those seen in real industrial hot-working tools. Based on their size and the extent of propagation, a clear distinction between primary, secondary, and craze cracks could be established at the failed surfaces. Additionally, a thermo-mechanical finite element model of the first 10 thermal fatigue cycles was developed to compute the transient temperatures, stresses, and strains distributions within the test specimen during thermal cycling. Based on the model results, the low cycle fatigue life was estimated using the Coffin–Manson equation, which relates the number of cycles to crack initiation to the plastic strain range per cycle. The experimentally obtained fatigue lives were appreciably shorter than the calculated ones, arguably due to surface roughness and oxidation effects.