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Among the manufacturing methods of high performance gradient functional materials, laser additive manufacturing technology can achieve the materials with gradient microstructure and property through precisely controlling the powder feeding and corresponding process adjustment, providing a new way to prepare high performance gradient functional materials more conveniently and efficiently. The basic principles and classification of laser additive manufacturing technology for high performance gradient functional materials were introduced in this paper, and the research progress in manufacturing high performance gradient functional materials by laser additive manufacturing technology at home and abroad was summarized. Furthermore, the shortcomings of this research field in material selection, process optimization and process monitoring were proposed, and its future research directions, such as the establishment of standard systems, in-depth theoretical research and the development of new manufacturing systems, were prospected, which provide guidance for the research of laser additive manufacturing technology for high performance gradient functional materials.

With the development of basic theoretical research and equipment, laser additive manufacturing technology is widely used in the manufacture of large complex components. However, the internal stress in laser additive manufacturing process tends to result in distortion and cracking. Stress and deformation control has become an urgent issue in laser additive manufacturing process. In this paper, research progress of residual stress in laser additive manufacturing was reviewed from various aspects such as residual stress forming mechanism, test methods, control measures. Furthermore, the main problems and research directions were proposed for the research of stress and deformation control technology, which provides guidance for the research of "shape control" in laser additive manufacturing.

Based on acoustoelastic theory, stress measurement of laser cladding coating with Rayleigh wave was investigated.The acoustoelastic formula for evaluation of stress in laser cladding coating was simplified by means of Taylor series expansion method.Combined with the static load tensile test, acoustoelastic coefficients were determined.The results show that the variation rate of Rayleigh wave signal velocity in Fe314 alloy coating increases linearly with the increase of stress.When tensile stress is greater than 495MPa, the variation rate of Rayleigh wave signal velocity does not change linearly any more.Based on the analysis of ultrasonic propagation theory and microstructure of laser cladding coating, the changing rule of acoustoelastic curve and its influence mechanism on stress measurement were analyzed, the inhomogeneous deformation of anisotropic laser cladding coating is the main cause of the "wave-type" fluctuation of acoustoelastic curve in high stress stage.Results show that anisotropic tissue effect can affect the result of stress measurement;the penetration in laser cladding layers can be ignored. By fitting the acoustoelastic curve, anisotropic tissue effect factor is determined.The experimental results show the maximum relative error in stress measurement is 4.4%, the method can realize the nondestructive evaluation of the stress in laser cladding coating.

Based on Lcr wave acoustoelastic theory, the influence mechanism of blind-hole on stress evaluation with Lcr wave was discussed. Combined with equivalent method, the blind-holes with different diameters were preset, the difference in time of flight between Lcr wave was calculated by cross correlation coefficient function, the Lcr wave acoustoelastic coefficient was determined with linear fitting function, the influence mechanism of blind-hole diameter on Lcr wave acoustoelastic coefficient was clarified based on the elastic plastic deformation theory and stress concentration theory of hole. The results show that when the diameter of blind-hole is different, the change rule of the difference in time of flight between Lcr wave is basically the same as stress increases, the difference in time of flight between Lcr wave increases linearly as stress increases, while the nonlinear feature is also gradually obvious, the maximum stress in linear stage is less than the yield strength of specimen, the Lcr wave acoustoelastic coefficient decreases gradually as blind-hole diameter increases, and it tends to be constant. The analysis shows that the stress concentration is seen as the main reason for above results, anisotropic structure of specimen and blind-hole depth are also the important reasons for that.

The temperature field of FeCrNiCu alloy forming layers of continuous wave(CW) and pulsed laser remanufacture was analyzed using the non-contact infrared thermometer.The general rule of temperature field distribution of molten pool and heat-affected zone of the two modes was obtained. The pulsed laser process superiority in heat input, forming deformation control and reducing the temperature in molten pool and heat-affected zone was vilidated. The results show that during pulsed laser forming the peak temperature in the heat-affected zone is 730.4-810.5℃,the peak temperature in the molten pool is 998.7-1383.4℃,which are all obviously lower than the same process of the CW mode; the temperature-rise rate and cooling rate of pulsed laser are higher, which is helpful to the forming of fine grain structures and good mechanical performance; the forming experiment also further verifies more narrow heat-affected zone in pulsed laser process.

Stress alone applied to ferromagnetic materials can induce the generation of weak magnetic signals on their surfaces, which can be potentially used to estimate the degree of damage of ferromagnetic components. In this paper, the normal component of stress-induced magnetic field, H p ( y ), was measured during tensile tests on the surfaces of sheet specimens of three ferromagnetic materials. It has been concluded that H p ( y ) depends on the applied stress and will present different characteristics on the elastic and plastic deformation stages, respectively. The phenomenon of sharp changes in magnetic signals occurring at the instant of fracture was also discussed from the view of the interaction energy in a ferromagnet.

The electro-brush plating technology is an important one in surface modification. The Ni-base plating coating reinforced by n-Al2O3 (noting as n-Al2O3/Ni composite coating), which the nano-grains dispersed evenly and combined tightly with matrix metal nickel, was prepared through adding nano-Al2O3 ceramic grains into the Ni-base bath. The experimental results illustrated that the micro-hardness and fretting wear-resistance of n-Al2O3/Ni composite coating were superior to that of the common rapid Ni-base plating coating. The reason was that the nano-Al2O3 ceramic grains changed the crystallizing condition of coating, so the coating was strengthened by fine-crystal intensification, high-density dislocation intensification and hard grains dispersion intensification.