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The impact damage evolution of thermally sprayed WC-Ni coatings was studied under 1-8000 impacts at a fixed load of 10 kN order. With increasing impact number, the accumulative damages of coatings evolve by in-sequence occurrence of WC spallation, coating cracking, and mixed coating/interface cracking accompanied with crack length and width growing. To comprehensively evaluate the coated component performance by observed accumulative damages as the failure criteria, a critical impact number Nc with critical load Lc is proposed for the onsets of different cracking features. The impact resistance is quantified, by Nc(Lcc) for onset of the coating cracking, and Nc(Lcm) for the mixed coating/interface cracking. A subclassification is identified as Nc(Lcm1) and Nc(Lcm2), respectively, for sequential occurrence of the isolated interface cracking and the propagated interface cracking of the penetrated from the coating surface. As the coating thickness is increased from 50 to 200 μm, the impact resistance under a load of 11.1 kN is correspondingly improved with Nc(Lcc) prolonged from 3000 to 4500, and Nc(Lcm1) from 4500 to 5000. In particular, Nc(Lcm2) is 6000 for the 50 μm coating, but no Nc(Lcm2) failure for the 200 μm coating up to 8000 impacts. The impact stress field analysis reveals reduced amplitudes of cyclic surface tensile stress and interface shear stress for the thicker coating, together with the interface shear stress shifting from a tensile-compressive alternating mode to a monotonous tensile one. The impact resistance of coated components under repetitive impacts is interpreted on thermodynamics where the thicker coatings mitigate impact mechanical energy dissipation of plastic strain energy in both coating and steel substrate, and accommodate larger reversible elastic strain energy during the periodic loading-unloading of impact cycles. [ABSTRACT FROM AUTHOR]

The impact resistance of coating/substrate systems is still lacking comprehensive understanding, especially for the thermal spray of wear-resistant coatings for coated components in potential applications with heavy-load impact service condition. The impact responses of a thermal spray WC-Ni coating/steel substrate were studied systematically by varying the coating thicknesses from 50 to 300 μm under an impact load of 1–10 kN. Besides conventionally employed crater depth/volume for impact evaluation, a critical impact load is identified to quantify the impact resistance with cracking. Considering the observed cracking modes, two critical loads of Lcc and Lcm have been defined corresponding to the cohesive failure of cracking in coatings and the mixed cohesive–adhesive failure including interface cracking, respectively. Increasing the coating thickness up to 200 μm raised the critical load Lcm from 7.4 to 11.1 kN, followed by a drop to 7.4 kN of Lcc at 300 μm. To reveal the influence of coating thickness, a major surface integrity parameter is proposed as the coating deformation in proportion to the total value of coating/substrate system in correlation to the impact resistance. The dependence of impact resistance on coating thickness is interpreted through the surface integrity changes by the thermodynamic mechanism of effective energy input and dissipation into the coating/substrate system from the external impact load. [ABSTRACT FROM AUTHOR]

Wear-yet impact-resistant demand is a big challenge for coated components under heavy-load service condition. To solve this high-performance manufacturing problem, a new strategy of design for manufacturing (DFM) with integrated design and processing is developed to incorporate processing effect on final performance via the pivot role of surface integrity. An impact performance model and the impact tester are constructed for a component with coated flat block/bulk cylinder mates for potential application in hydraulic machinery. A WC-12Ni/Ni60A two-layer coating on 17-4PH martensitic steel substrate is designed with thermal spray process. Impact crater depth, surface hardening, and residual stresses are identified as major surface integrity parameters determining wear/impact performance by the modeling with testing. The design parameters of geometry, material, and structure are quantitatively linked to the final performance by a process signature (PS) correlative analysis on the identified surface integrity to internal material loading of plastic/elastic strain energies. The PS correlation posts coating thickness as a high-sensitivity parameter for design, facilitating a buffering effect of reduced peak stresses among the coating-substrate system. The DFM optimization is understood by irreversible thermodynamics as reducing energy dissipation of the internal material loading from the external impact loads. The manufacturing inverse problem is thus solved by material-oriented regularization (MOR) on the homologous PS correlations integrating the design and processing phases. The manufactured component, with optimal Ni60A interlayer thickness of 75-100 µm at a top WC-12Ni coating of 200 µm, achieves a desired performance of up to 6000 impacts under a nominal load of 15 kN. [ABSTRACT FROM AUTHOR]