J.Z. Lu

Simulation, analysis and validation of residual stresses on LY2 aluminium alloy by laser shock processing with elliptical spot

Abstract The effects of laser shock processing on the residual stresses of the LY2 aluminium alloy samples with elliptical spot (long axis length, 12 mm; short axis length, 3 mm) were experimentally investigated, and the effects of the overlapping rate on the residual stresses were simulated using the Abaqus software. The simulated residual stresses were basically in agreement with the measured data, and the relationship between the magnitude and uniformity of residual stress and the overlapping rate was also addressed. Results show that the largest stress magnitudes are located on the top surface of the sample, and the greatest uniformity is achieved by the overlapping of elliptical laser spots. The overlapping rate is critical for the uniformity of the residual stress across the surface. Within a certain impact number range of one to four times, increasing the shocked number can increase the magnitude of residual stress near the surface but not effectively increase the plastically affected depth.

Phases Transformation Analysis of ZrO2 Ceramics after Laser Shock Processing

Through phrase transformation analysis on ceramics samples after applied laser shock wave, study was made on micro-structure and mechanical performance transformation and transformation laws. Thus conclusions were drawn through analysis as follows: tensile stress was caused on back surface of TZP ceramics sample by laser shock wave, and further transformation was generated under tensile stress in a way that about 48% tetragonal phrases t-ZrO2 transformed into monoclinic phrases m-ZrO2, which expanded volume of and gave rises to micro-cracks, and relief stress and micro-cracks caused will absorb the energy of main cracks, which can impede expansion of main cracks and realize the aim of phrase transformation toughening.

Experiment study on CO2 laser cleaning rubber sulfuring mould

Parameters and mechanisms of cleaning rubber layer from a rubber sulfuring mould with CO2 laser are analyzed. Laser cleaning is a non-abrasion way, and it can improve mould service life. There are cleaning threshold and damage threshold in laser cleaning, and cleaning percentage of the surface increases with laser power density. The effects of laser parameters on cleaning and performance of the cleaned surfaces are studied. The results show that pulse laser can remove rubber layer completely under proper parameters when the value of laser cleaning threshold is 5~35J/cm2, and no damages are found on substrate surface, mould abrasion that is cleaned by laser decreased.

Nondestructive measurement of the residual stress TiN thin film coated on AISI 304 substrate by x-ray stress analyzer

Titanium nitride films are deposited on AISI 304 steel with a hollow-cathode-discharge (HCD) ion-plating technique. The status of residual stresses in TiN thin film coated on AISI304 substrate by HCD is studied by x-ray diffraction stress analyzer. By analyzing morphology of the residual stress of TiN thin film at interface between TiN film and AISI 304 substrate, the adhering mechanism of TiN thin film is understood as follows: the mechanical interlocking had important contribution to the adhesion strength, the thermal stress is the major factor which resulting TiN thin film peeling off spontaneously. The results show that the value of thin film is -210MPa~-650Mpa, and the thermal stress is compressive, the intrinsic stress is tensile, origins of the residual stress are primarily discussed.

The Microstructure and Properties of LY12 Aluminum Alloy by Ultra-High Plastic Strain

The ultra-high plastic deformation behavior by laser shock processing on the LY12 aluminum alloy had been investigated. The morphology of the materials had been analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the grain refinement layer was formed in the thickness of about 100μm .The dislocation density of LY12 aluminum alloy should be large increased after laser shocking because the accumulation of dislocation was appeared on the grain boundary. With the laser energy density increased there formed subgrain structure and eventually generate ultra-fine grain. Hardness test results also show that the surface hardness obtains a big growth about 60% after laser shock processing. The results showed that the formation of ultra-high plastic strain can improve the surface hardness of LY12 aluminum alloy, and thus effectively improve the comprehensive mechanical properties.

Numerical Simulation and Calculation of the Temperature Field during Laser Surface Melting the Pure Al

Temperature field during laser surface melting the pure Al was numerically simulated by the Laplace integral transform technique using the MathCAD software. The influences of laser power densities on the surface temperature of the pure Al were analyzed. Mathematical expressions for the temperature distribution of the heating and cooling process on the pure Al surface were obtained.

Friction Behaviors of SiC Particle-Reinforced Cu Matrix Composites

SiC particle reinforced Cu composite was fabricated by powder metallurgy and hot extrusion process. The friction behaviour of pure Cu, braze and composites was studied on a block-on-ring test. The blocks were slid against 40Cr steel rings under the lubrication of 232# machinery oil. It shows that the wear rate of pure Cu is about then times of the 5 vol.% Cu composite at a normal load of 300 N. The satisfied wear resistance prove the SiC is a promising reinforcement material for Cu matrix composite. However, the 20 vol.% SiC did not exhibit prospected wear resistance. The discussion of this phenomenon was conducted.

Experiment of Laser Shock Processing on AISI 8620 Alloy Steel

Laser shock processing (LSP, also known as Laser shock peening) is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. LSP is proved to be superior to conventional treatments such as shot peening in many engineering products. This paper focuses on Laser shock processing and its effects on mechanical properties of material AISI 8620 alloys steel. Experiment results indicated that compared with base material, the surface hardness increased by 13.8%, and compressive residual stress increased by 521%. Statistical method was introduced to analyze hardness and residual stress change before and after the LSP.

Microstructure of Laser Cladded Cobalt-Based Alloy Coating on T10 Tool Steel

Co-based alloy coating was fabricated by powder feeding laser cladding on T10 tool steel. The microstructure and phase composition were investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results showed that the different solidification microstructures on the section, such as planar, cellular and dendrite formed from the interface to the surface. The main phase γ-Co and another phase Cr23C6 existed in the original coating, however, the main phase γ-Co was unchanged, and another phase was replaced by Cr7C3 accompanying with Co3C and Co4B precipitations after aging treatment.

Study on the Properties of the Laser Cladded Cobalt-Based Alloy Coating on T10 Tool Steel

Co-based alloy coating was cladded on T10 tool steel by the powder feeding and continuous CO2 laser. The results showed that compared to the unreinforced T10 tool steel substrate, the microhardness of the Co-based reinforced composite was significantly enhanced and the maximum value was existed in the middle of the cladding coating. The corrosion resistance of the cladding coating was also improved. After cryogenic treatment, there is no obvious change for the structure of the cladding coating while the phase is transformed, leading to an increase in the microhardness of the cladding coating.