Refractive Index of Heavily Germanium-Doped Gallium Nitride Measured by Spectral Reflectometry and Ellipsometry

Gallium nitride (GaN) doped with germanium at a level of 1020 cm−3 is proposed as a viable material for cladding layers in blue- and green-emitting laser diodes. Spectral reflectometry and ellipsometry are used to provide evidence of a reduced index of refraction in such layers. The refractive-index contrast to undoped GaN is about 0.990, which is comparable to undoped aluminium gallium nitride (AlGaN) with an aluminium composition of 6%. Germanium-doped GaN layers are lattice-matched to native GaN substrates; therefore, they introduce no strain, cracks, and wafer bowing. Their use, in place of strained AlGaN layers, will enable significant improvements to the production process yield.

Evaluation of the quality of three-layer steel bimetallic strips obtained on a unit of continuous casting and deformation

Today there is an urgency of creating high-performance continuous processes for the production of bimetals. The article describes the main tasks of improving the quality of the materials under consideration. Two stages of the technology for producing steel three-layer bimetallic strips on the unit of a combined continuous casting and deformation process are considered. The authors give recommendations on the conduct of the technological process in order to obtain high-quality bimetallic strips on such unit. The problem statement is presented. The material considers initial data for determining the temperature of the steel base strip and the stress-strain state of the metals of the cladding layers and the strip in deformation center of a three-layer bimetallic ingot. A model for calculating and a method for solving problems of thermal conductivity and elastoplasticity are shown. Regularities of the temperature change of the main steel strip are given during its passage through the molten metal of the cladding layer. Stress-strain state of the metals of the main strip and cladding layers in the deformation center was determined when three-layer bimetallic steel strips were obtained on the unit of combined continuous casting and deformation process. The authors describe the values of compression of the main steel strip and mutual displacement of the layers during compression of the bimetallic ingot by the strikers. Regularities of the distribution of axial and tangential stresses are shown along the contact line of the cladding layer with the striker. The evaluation of the process of obtaining bimetal steel 09G2S - steel 13KhFA - steel 09G2S was made on a pilot unit for continuous casting and deformation. Microstructure of the main strip and cladding layers of a three-layer bimetallic steel strip is shown when a combined continuous casting and deformation process is obtained in one unit.

Optimization for Morphology of Grinding Layer on Textured Laser Cladding Grinding Tool

In order to improving the grinding performance of laser cladding textured grinding tool (LCTGT) under high speed grinding process, the topography shape (height, width and height/width ratio) of laser cladding grinding layers on LCTGT were designed with RSM (response surface method) through optimizing laser cladding processing parameters and laser cladding layers structure parameters that based on Archimedes helix coefficients. The LCTGTs were produced with optimized laser cladding parameters and structural parameters for laser cladding grinding layers. The results showed that laser cladding parameters of 397W of laser power, 3.56 mm/s of the laser scanning speed and 0.91 r/min of powder feeding rate and structure parameters of laser cladding layers of 6-10-10 can meet requirement.

Experimental Study on the Properties of Copper Base Alloy by Laser Cladding on the Surface of Pure Copper Contact

Arc ablation is the main reason for the failure of pure copper switches. In order to improve the electric ablation resistance of pure copper contacts, Cu-W-Ni alloy cladding layers with different tungsten contents were prepared on the surface of pure copper matrix by laser cladding technology. The microstructure, composition distribution, hardness and corrosion resistance of the cladding layer were analyzed. The results show that the surface of the cladding layer and the pure copper matrix is metallurgical, without holes, cracks and other defects, and the dilution rate is low, and the average hardness is significantly increased. On the whole, the comprehensive properties of CuW10Ni3 cladding layer are slightly better than the other two Cu-W-Ni cladding layers. Compared with the pure copper matrix, the contact hardness is significantly improved under the premise of ensuring the electric conductivity of the inner pure copper matrix.

Deposition of Nickel-Based Superalloy Claddings on Low Alloy Structural Steel by Direct Laser Deposition

In this study, direct laser deposition (DLD) of nickel-based superalloy powders (Inconel 625) on structural steel (42CrMo4) was analysed. Cladding layers were produced by varying the main processing conditions: laser power, scanning speed, feed rate, and preheating. The processing window was established based on conditions that assured deposited layers without significant structural defects and a dilution between 15 and 30%. Scanning electron microscopy, energy dispersive spectroscopy, and electron backscatter diffraction were performed for microstructural characterisation. The Vickers hardness test was used to analyse the mechanical response of the optimised cladding layers. The results highlight the influence of preheating on the microstructure and mechanical responses, particularly in the heat-affected zone. Substrate preheating to 300 °C has a strong effect on the cladding/substrate interface region, affecting the microstructure and the hardness distribution. Preheating also reduced the formation of the deleterious Laves phase in the cladding and altered the martensite microstructure in the heat-affected zone, with a substantial decrease in hardness.

Structure and Properties of Ti-Al-Ta and Ti-Al-Cr Cladding Layers Fabricated on Titanium

Being one of the most high-demand structural materials, titanium has several disadvantages, including low resistance to high-temperature oxidation and wear. The properties of titanium and its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thick Ti-Al-Ta and Ti-Al-Cr layers were obtained on titanium workpieces by a non-vacuum electron-beam cladding. The microstructure and phase compositions of the samples were different for various alloying elements. The Cr-containing layer consisted of α2, γ, and B2 phases, while the Ta-containing layer additionally consisted of ω′ phase (P3m1). At the same atomic concentrations of aluminum and an alloying element in both layers, the volume fraction of the B2/ω phase in the Ti-41Al-7Ta alloy was significantly lower than in the Ti-41Al-7Cr alloy, and the amount of γ phase was higher. The Ti-41Al-7Cr layer had the highest wear resistance (2.1 times higher than that of titanium). The maximum oxidation resistance (8 times higher compared to titanium) was observed for the Ti-41Al-7Ta layer.

All-phase fast Fourier transform and multiple cross-correlation analysis based on Geiger iteration for acoustic emission sources localization in complex metallic structures

Nowadays, the localization and identification of acoustic emission (AE) source is widely utilized to structural health monitoring (SHM) of complex metallic structures. However, traditional AE source localization methods are generally difficult to localize and characterize AE sources in plate-like structure that has complex geometric features. To alleviate the problem, a novel AE source localization method based on all-phase fast Fourier transform and multiple cross-correlation analysis is proposed in this article. Moreover, least squares and Geiger iteration algorithm are applied to determine the coordinates of AE sources. In addition, an improved Bayesian information criterion (BIC) version named autoregressive BIC (i.e., AR-BIC) is presented to increase the accuracy of source localization. To validate the performance of the proposed approach, the classical pencil lead break tests are carried out on a 316 L stainless steel with 10 laser cladding layers. Experimental waveforms are generated from AE sources near laser cladding layers, the surface of the structure, and on its edges. Additionally, to evaluate the performance of the proposed approach in three-dimensional AE source localization, an industrial storage tank is used to acquire three-dimensional AE sources through manually striking. Finally, to further verify the effectiveness of the proposed approach, comparisons with conventional AE source location methods (i.e., PAC or SAMOS AE acquisition system, Newton’s method, and multiple cross-correlation based on Geiger algorithm) and two representative approaches (i.e., deep learning and Bayesian methodology) for localizing AE sources generated by complex metallic structures are conducted. The comparative results demonstrate the effectiveness and superiority of the proposed method in AE-based SHM of complex metallic structures.

Oxidation resistance and stress corrosion cracking susceptibility of 308L and 309L stainless steel cladding layers in simulated PWR primary water

Exposure and slow strain rate tensile (SSRT) tests were conducted in a simulated pressurized water reactor (PWR) primary water to investigate the oxidation resistance and SCC susceptibility of 308L and 309L stainless steel (SS) cladding layers. A double-layer structure oxide layer grown on 308L SS and 309L SS contained the Cr-enriched nanocrystalline internal layer and the Fe-enriched spinel oxide in the external layer. Ni-enrichment at the matrix/oxide (M/O) boundary was observed. The internal oxide film on 309L SS was thicker and had a lower Cr content than that on 308L SS. Preferential dissolution of inclusions led to pits on 308L SS and 309L SS surfaces during the exposure tests. More inclusions in 309L would decrease its SCC resistance due to the pits can act as the SCC initiation site. 308L SS had a lower susceptibility of SCC than 309L SS in PWR primary water. Lower ferrite content, higher strength/hardness reduced the oxidation and SCC resistance of 309L SS cladding. The effect of ferrite on oxidation and SCC of the SS claddings was discussed.

Microstructure Evolution Mechanism of Single and Multi-pass in Laser Cladding Based on Heat Accumulation Effect for Invar Alloy

This work explores how the process parameters in laser cladding affect the evolution of the microstructure of the single pass and multi-pass cladding layers of Invar alloys. The research examined the cladding layers from three aspects: (1) the transformation of grain size, HAZ width, ratio of the columnar crystal to the equiaxed crystal, and change of Fe content of cladding layer; (2) the effects of heat accumulation on grain size, HAZ width and remelting zone; and (3) the hardness distribution of single pass and multi-pass cladding layers. The investigation has the following four findings: (1) the cladding layer is composed of equiaxed crystals at the top and columnar crystals at the bottom of cladding layer; (2) the processing parameters have significant effects on the width of the HAZ, proportion between the columnar and equiaxed crystals and the change of Fe content of cladding layer. (3) the gradual accumulation of heat causes the increase in HAZ width, the grain size, and the area of the remelting zone; and (4) the hardness progressively reduces from the top to bottom along the direction of the centerline of the cladding layer.