Narrow Results

An infrared CO₂ laser was used for regional heating to study the heating effect on hot filament chemical vapor deposition of diamond-like carbon formation on Si(100) face substrates. The substrate surface temperature was about 450–500°C. The power of the laser called low, medium, and high raised the temperature of the substrate locally by 25, 45, and 55°C, respectively. At medium laser power, at the central laser beam region, a narrow Raman peak centered at 1438 cm^-1 was detected. It can be concluded that this region has good-quality DLC. This moderate high-frequency peak corresponds to a fourfold-rotation-symmetry atom in an amorphous carbon network from the tight-binding molecular dynamics simulation of Wang and Ho.

A micron-sized WC-CrCo powder was coated onto an IN718 substrate using high-velocity oxy-fuel (HVOF) thermal spraying. To further improve the surface properties, the HVOF coating was heat-treated by a CO₂ laser. The surface properties of both the coating and the laser-heated coating were then compared. The HVOF optimal coating process (OCP) for a coating with the highest surface hardness was determined with the Taguchi program. The friction and wear behaviors of the coating, an electrolytic hard chrome (EHC)-plated coating and IN718, were comparatively investigated via a reciprocating sliding wear test at both 25 and 450°C. The friction coefficient (FC) for all three samples decreased when the sliding surface temperature increased from 25 to 450°C. The FC of the coating decreased with increasing surface temperature: 0.33 ± 0.02 at 25°C to 0.26 ± 0.02 at 450°C; the coating had the lowest FC among the three samples. At both temperatures, the coating wear depth (WD) was smaller than those of the EHC sample and IN718. At room temperature, WC-CrCo and the EHC coatings had good wear resistance and had only a shallow WD. IN718, however, had poor wear resistance with 50 μm deep grooves created from fretting corrosion that arose during the 1500 reciprocating slides (2.5 Hz, 10 min sliding wear test). At 450°C, the coating WDs were much shallower than those for the EHC coating and IN718: 0.5-μm deep grooves compared to 60–70-μm deep grooves. These results proved that the coating provided a protective coating for IN718 and other metal components. With the OCP coating fabricated from the powders on the IN718 surface, the surface hardness increased 316% from 399 Hv to 1260 Hv. Furthermore, by laser heating the coating surface for 0.6 s, the hardness increased 44% from 1260 ±30 Hv to 1820 ±100 Hv, porosity decreased more than five times from 2.2 ± 0.3% to 0.4 ± 0.1%, and the coating thickness decreased 17% from 300 to 250 μm. These results showed that both the WC-CrCo powder coating and the laser-heating improved the surface properties of IN718.

A numerical study is performed on the effect of laser radiation on the propagation phenomenon of a thermal wave in a very thin film subjected to a symmetrical heating on both sides. Laser heating is modelled as an internal heat source. The non-Fourier, hyperbolic heat conduction equation is solved by a numerical technique based on MacCormack's predictor-corrector scheme. Consideration is given to the time history of heat transfer behaviour before and after symmetrical collision of wave fronts from two sides of a film. It is disclosed that (i) if the absorption coefficient of the laser increases, temperature overshoot causes in a very thin film within a very short period of time, and (ii) the overshoot and oscillation of thermal wave depend on the frequency of the heat source time characteristics. This trend becomes minor in a thick film.

A semi-analytical solution of bio-heat conduction on the three-layer skin is presented. The performance of the typical heat treatment (heating by laser and cooling by fluid at skin surface) is studied. The transient temperature field and thermal damage of skin are investigated. Effects of several parameters on temperature variation and thermal damage are discussed. The results of the paper will be useful for heat therapy in clinics. In addition, the presented result is very consistent to that by the finite element method. The semi-analytical method can be easily applied for solving the general problem of heat conduction in any multilayer structure.

Dimension precision plays an important role in precision machining. The two-dimensional ultrasonic vibration cutting (TDUVC) method reduces cutting force and alleviates tool wear, meanwhile, laser assisted cutting (LAC) improves the material workability under high temperature. In this paper, laser heating and two-dimensional ultrasonic vibration were combined in cutting of tungsten carbide (YG10) to improve machining dimension precision. According to the experimental results, a prediction model of machining dimension was built based on time series model. The results show that the machining dimension precision is improved significantly in laser and ultrasonic composite assisted cutting (LUAC), and AR (2) and AR (12) of time series model predicts machining dimension with high precision (the relative error is less than 10%), and reflects tool wear state. Moreover, comparison with artificial neural network (ANN) also proves that the time series model is more suitable for the prediction of machining dimensional in LUAC.

The effect of laser, as a heat source, on a one-dimensional finite living tissue was studied in this paper. The dual phase lagging (DPL) non-Fourier heat conduction model was used for thermal analysis. The thermal conductivity was assumed temperature-dependent, resulting in a nonlinear equation. The obtained equations were solved using the approximate-analytical Adomian decomposition method (ADM). It was concluded that the nonlinear analysis was important in non-Fourier heat conduction problems. Moreover, a good agreement between the present nonlinear model and experimental result was obtained.

In this paper, the laser short-pulse heating of a solid surface is considered. The time fractional heat conduction model is used as the constitutive heat diffusion model and the corresponding fractional heat conduction equation is built. Inverse Laplace transform is applied to obtained the analytical solution for the unit step pulse laser. The numerical results are presented graphically for various values of fractional order parameters. Fractional order parameter not only influence magnitude of temperature rising, but also the velocity of heat propagation. This research provides some new points for further studying laser heating or other non-Fourier heat conduction problems.