A Study Of Thermal Damage For Laser Cladding Technology And Its Detection

Laser cladding is a complicated thermal-physical process of the interaction of laser beam,cladding material and substrate material, involving phase transition theory, thermodynamics andkinetics theory as well as constitutive relations deductive theory under thermal process, as a result, thefactor that affects the usage performance is also complicated. This paper carried out a comprehensivestudy on thermal damage consequent to laser cladding, as well as its detection. Detailed works arelisted:First, a deep analysis on the microstructure and metallographic morphology of the material wascarried out based on the phase transition theory, the result showed a localized variation ofmicrostructure. The cladding layer is mainly formed by the mixture of fine columnar crystal andequiaxed crystal, homogeneous on the whole; while the substrate workpiece is divided into three partsas remelt zone, heated affected zone and unchanged base material decided by the heat affection degreeof laser beam.Then, thermal field and stress field under different cladding parameters was studied takingadvantage of the finite element software ANSYS based on thermal-mechanical theory. It reveals anobvious relationship between maximum temperature, cooling rate, residual stress and the processparameters. The residual stress mainly appears as tensile stress, which the maximum value is almostthe degree of yield stress. In addition, the stress mainly acts in longitude and transverse direction ofthe cladding pass while in the depth direction the stress is barely small.Finally, after demonstration of cladding thermal damage by tension and fatigue test, a generalscalar model was suggested to quantify thermal damage benefited from the present works on theverification of thermal damage. Study of some of the damage factors shows that the damage related tocladding parameters tightly.In the end of the thesis paper, the author has made a trial to detect the thermal damage forremanufactured products using metal magnetic memory (MMM) technology. The result reveals thatthe change of the intrinsic scattering magnetic field signals can reflect the fatigue damage, as well asthermal damage.The achievement of this paper is of great significance to the assessment of thermal damageinduced by laser cladding, while the implementation of the proposed model is likely to promote theassessment of structure remaining life in a large extent.