Mechanical Properties And Damage Mechanism Of Laser Cladding Particle Reinforced Composite Coatings

Due to its high strength, high temperature resistance and good wear resistance, the lasercladding composite coatings has been widely used as mechanical parts and components in thespecial and harsh field such as machinery manufacturing, petrochemical, nuclear engineering,automotive industry, aerospace. However, some kind damages of composite coatings suchparticle broken and particle/matrix interface debonding will occur under different loadingconditions. On the other hand, the defects of composite coatings such as micro-void introducedduring preparation will accelerate the failure of material. Further and deeper researches on themechanical properties and damage mechanism of laser cladding composite coatings werenecessarily required.In this dissertation, macro-mechanical properties and micro-damage mechanism of lasercladding H13-TiC composite coatings has been studied. The mechanical properties of particleand matrix phases at the microscopic scales were measured by nanoindentation. The particlecracking induced by nanoindentation was observed and the critical fracture strength of particlewas obtained by the combination of experiment and finite element analysis. Based on themicromechanics, elastic-plastic mechanics and experimental results, a new damage constitutivemodel of composite coatings was presented. The model was embedded in the finite elementsoftware ABAQUS subroutine UMAT, focusing on investigation of damage and failurebehavior of composite coatings. The research work will provide theoretical, numerical andexperimental support for the preparation of laser cladding composite coatings. The main workand achievements are as follows:1. With appropriate laser processing, the H13-TiC composite coatings was cladded on the H13die steel. The mechanical properties of composite coatings containing different particlevolume were obtained by uniaxial tensile experiment. The initial and evolution microstructureof material as well as damage mechanism were observed by scanning electron microscopy(SEM). The results showed that micro-defects such as micro-void were introduced duringpreparation, particle fractures was the main reason of crack formation in the composite coatings,the particle/matrix interface debonding appeared in the later tensile experiment. Such resultsprovided the experimental basis of damage model.2. The mechanical properties such as hardness and modulus of TiC particle and H13matrixwere measured by nanoindentation. In addition, the influence of distance between indentationposition and particle center, indentation depth and the particle morphology on the indentationresults were investigated; The critical fracture stress of TiC particle was obtained by thecombination of experiment and finite element analysis characterizing of the strengthmeasurement of ceramic particle.3. The elastic-plastic properties of composite coatings with different particle volume werestudied by Mori-Tanaka mean-field homogenization scheme. Based on the experimental results,the parameters of Weibull damage principal, which characterized the damage mode of particle,were obtained.4.Coupling Mori-Tanaka(M-T) mean-field homogenization scheme with theGologanu–Leblond–Devaux (GLD) yield criterion, the damage model accounting for theeffect of void shape, void size, void volume and particle damage on tensile behavior oflaser-processed composite coatings was developed. At last, the prediction results of this modelwas compared with experimental results, and the consistence demonstrated that the model welldescribed the damage process of laser cladding composite coatings.