Laser assisted machining technology can heat and soften metals, which can be used for improving the machinability of superalloys such as Ti6Al4V and Inconel718. Researches on temperature field simulation of Ti6Al4V and Inconel718 are conducted in this paper. A thermal differential equation is established based on Fourier’s law and energy conservation law. Then, a model using ABAQUS for simulating heat transfer process is brought out, which is then experimentally validated. Using the simulation model, detailed investigations on temperature field simulation are carried out in Ti6Al4V and Inconel718. According to simulation, surface temperature of the two superalloys eventually reaches their peak values, and the peak temperature of Ti6Al4V is much higher than that of Inconel718. To further investigate temperature heated by laser, laser parameters such as power, scanning velocity, laser spot radius and inclination angle are set to be variables separately for simulation. Simulation results show that laser power and laser spot radius are predominant factors in heating process compared with the influence of scanning velocity and inclination angle. Simulations in this paper provide valuable references for parameter optimization in the following laser heating experiments, which plays an important role in laser assisted machining.
Nanoindentation is a good method for characterizing residual stresses with large gradient that distributed in a very
confined area. In our previous research, a formula was brought out to characterize residual stresses from elastic modulus
measured in nanoindentation experiments. In this paper, aluminum alloy bulks were used as samples to validate the
formula. The bulks were machined to be mirror surface on one side through ultra-precision diamond turning. Two
samples were compressed and stretched by load instruments respectively. Nanomechanical properties such as elastic
modulus in the areas on the mirror surface of the compressed and stretched samples were both measured by a
commercial nanomechanical test system (TriboIndenter, Hysitron Inc.). Using the formula, then, the mean values of
residual stresses on the mirror surface were calculated through the acquired experiment data. After that, the two stressed
samples were tested by a commercial XRD instrument (X'Pert, Philips Inc.). Comparing the residual stresses that
obtained through nanoindentation and XRD methods, their difference was no more than 10.5%, which showed that the
formula is suitable for characterizing residual stresses in materials even it has high plasticity. Thus, the formula was
As an excellent micromachining method, femtosecond laser ablation is more and more frequently used in
micromachining. Femtosecond laser ablation can take residual stresses beside the machining area, which may affect the
performance of micro devices. In this paper, grooves were ablated by femtosecond laser and nanoindentation
experiments were exploited to uncover residual stresses in the area beside the grooves. The reduced modulus and
hardness in different areas around the groove were measured through nanoindention and position dependent regular
changes in reduced modulus were found. Such changes contained the information of residual stresses in such area. A
formula correlating residual stresses with the reduced modulus was set up.
When femtosecond laser pulses are tightly focused on transparent material, high pressure caused by temperature increase in a confined volume of material will result in microexplosion. Thus the materials in such area will be densified, which causes the variation in refraction index. Continuous explosive lines that are just under the surface of quartz crystal wafers are micromachined by femtosecond lasers. These lines can serve as optical waveguides. Surface morphologies and nanomechanical properties in the area above the explosive lines were measured. The surface irradiated by laser beam is much rougher than that of the unirradiated zone, and there is a clear boundary between laser-induced rough and smooth areas. The size of the rough areas is much smaller than the laser spots that are irradiated on the surface. Nanomechanical changes occur in the area that has no observable damages in microscope and AFM. The position dependent variations of mechanical properties around the surface area that is just above the irradiated line were described in this paper. The values of elastic ratio changes significantly in different positions, which reveals the position dependent variations of femtosecond laser induced stresses and structural changes. Shocks generated during microexplosive process response for such changes. The changes can cause the variation in the degree of densification in different positions, which is corresponding to the modification of refractive index. By focusing the femtosecond laser pulses into the bulk of quartz crystal, internal waveguides and grating structures were fabricated.