激光模具表面强化的应用研究

介绍了激光表面非熔凝加工的特点及应用、国内外激光表面非熔凝加工的发展与研究现状,以及激光模具表面强化存在的问题及今后的研究方向。     

激光模具表面非熔凝加工的应用研究

通过建立试件的热分析模型,对激光模具表面非溶凝加工过程进行了有限元分析,从而对激光相为硬化过程中的温度场、残余热应力、应变场进行了研究。通过计算机模拟,获得指导性工艺参数,并对式件进行激光强化试验,将计算值与试验值进行耦合,从而获得最佳工艺参数,提高模具的使用寿命。     

激光模具表面非熔凝加工的应用研究

通过建立试件的热分析模型,对激光模具表面非熔凝加工过程进行了有限元分析,从而对激光相变硬化过程中的温度场、残余热应力、应变场进行了研究。通过计算机模拟,获得指导性工艺参数,并对试件进行激光强化试验,将计算值与试验值进行耦合,从而获得最佳工艺参数,提高模具的使用寿命。     

激光相变硬化在模具表面强化中的应用研究

介绍了激光表面相变硬化加工的特点及应用、材料表面激光相变硬化工艺的研究———激光相变硬化机制、激光相变硬化层的影响因素、激光相变硬化过程的温度场研究、激光相变硬化后残余应力场的研究以及激光相变硬化在模具表面强化中的应用     

激光相变硬化在模具表面强化中的应用研究

介绍了激光表面相变硬化加工的特点及应用、材料表面激光相变硬化工艺的研究——激光相变硬化机制、激光相变硬化层的影响因素、激光相变硬化过程的温度场研究、激光相变硬化后残余应力场的研究以及激光相变硬化在模具表面强化中的应用。     

人工神经网络技术在成形模具表面激光强化中的应用

基于人工神经网络基本理论，建立在成形模具表面激光强化中预测材料表面最高温度、强化效果的BP网络模型，借助于MATLAB仿真软件中的神经网络工具箱作为开发平台，将试验样本数据和经过试验验证的数值计算结果作为补充的样本数据用于BP网络的训练，利用训练好的BP网络对非线性的样本数据规律进行拟合，实现激光加工工艺参数的优化，为实际生产和加工提供有效的依据。     

激光表面强化技术介绍

从激光相变硬化、激光表面熔敷、激光合金化等几个方面,介绍了激光表面强化技术以及基本原理、方法和应用实例。     

工模具材料激光表面强化处理应用与发展

介绍了激光表面淬火、激光表面熔覆、激光表面合金化、激光熔凝的特点和在工模具材料上的应用.通过激光强化处理改善了工模具材料表面硬度、耐磨性、抗疲劳等力学性能.最后指出了实际应用中存在的问题及今后需要深入研究的方向.     

连续激光强化模具刃口的工艺研究

简述了激光强化模具刃口的机理和工艺图，提出了强化工艺参数选择的原则、方法和步骤。     

模具激光强化处理技术

模具激光强化处理具有弥散强化的性能优势,对淬透性依赖性小的材料优势,表层压应力的工艺优势,铸铁激光淬火独特的强化机理,局部强化和大型模具强化的技术优势,可实现组合模具单体化,代替化学热处理,低成本材料代替高成本材料,为提升模具制造业技术水平搭建新平台。     

Excimer laser surface treatment of plasma sprayed alumina-13% titania coatings

Surface modification of engineering materials allows the production of far superior products in terms of reduced wear, increased corrosion resistance, better biocompatibility, and improved optical and altered electrical/electronic properties. Excimer laser annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, alumina-13% titania (AT-13) coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed parametric study was performed to investigate the effects of different parameters such as laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the mechanical properties, surface morphology, and microstructure of the coatings. The study reveals that the laser fluence plays a major role in modifying the surface morphology of the coating, followed by the pulse repetition rate.     

Pyrometry in laser surface treatment

The pyrometers specially developed for laser machining were applied to analyse temperature fields in laser cladding. It is shown that 2D temperature mapping is useful to optimise the cladding parameters: zone of powder injection in relation to laser beam, temperature gradients and their evolution versus cladding parameters. Multi-wavelength pyrometer was applied to restore the value of true temperature that is useful to control melting/solidification when complex powder blends are used and when it is necessary to minimise thermal decomposition of certain compounds. The developed multi-wavelength pyrometer and the applied notch filters are appropriate instruments to measure the evolution of surface temperature produced by Nd:YAG laser pulses of millisecond duration. The variations of several characteristics of the thermal cycle, such as the maximum peak temperature, T_max, the instant when melting starts, t_m, the melt lifetime, τ_lt, the duration of the solidification stage, τ_s, with various energy inputs (in the range 10-33 J) and pulse durations (10-20 ms), have been determined for rectangular laser pulses. By appropriate modification of the laser pulse shape (keeping the same energy input and pulse duration), it is possible to realise rather different temperature profiles to vary the melt lifetime and the instant when melting starts. In order to minimise surface temperature variation, to minimise thermal decomposition of certain melt compounds and to increase the melt lifetime, it is necessary to apply higher energy density flux at the beginning of the laser pulse. To obtain a higher peak of the surface temperature, for the given energy input and pulse duration, it is necessary to apply higher energy density flux at the pulse end. This will minimise the melt lifetime as well. In general, it is possible to impose the instant when melt cooling starts and thus to realise an intensive melt cooling during laser irradiation. The above results correspond to the action of laser pulses in the millisecond range with relatively low energy density flux (4 · 10⁸-10⁹ W m^− 2) on metallic materials, whose thickness is larger than the heat affected zone (i.e. semi-infinite body from the heat transfer point of view).     

Cemented carbide surface modifications using laser treatment and its effects on hard coating adhesion

A pulsed HyBrID copper laser (510 nm, 30 ns, 13.8 kHz) was used for the treatment of cemented carbide substrate before deposition of TiCN/Al₂O₃/TiN coating by the MT-CVD process. The influence of the laser treatment on the surface morphology, surface structure and coating adhesion was investigated based on the laser irradiation dynamics used here. The experimental results showed that a large variety of cemented carbide surface textures could be obtained, depending on the laser intensity and number of applied laser pulses. Moreover, this laser process was found to produce some less carbon non-stoichiometric WC phases such as β-WC_1 − x and α-W₂C. Finally, using the Rockwell C adhesion test as output criteria, two sets of laser parameters were identified that produced a surface with adhesion strength comparable to that of commercial tools pretreated by micro-sandblasting.     

Surface vitrification of alloys by laser surface treatment

With laser surface treatment (LST) method, the surfaces of Zr-, Cu-, Fe- and Al-based alloys were melted and amorphous or amorphous-crystalline composite structures were synthesized, which were related to the different glass-forming ability of the alloys. Influences of laser processing parameters on glass formation for Cu₆₀Zr₃₀Ti₁₀ alloy were investigated and the laser treated alloy exhibited a gradient structure: amorphous surface, amorphous-crystalline composites transitional region and crystalline substrate. Temperature distributions and thermal profiles of the treated Cu₆₀Zr₃₀Ti₁₀ alloy during the laser process were simulated using finite volume method. The formation mechanism of the gradient structure is discussed based on the experimental and simulated results.     

Microstructure, mechanical and wear properties of laser processed SiC particle reinforced coatings on titanium

Laser processing of Ti-SiC composite coating on titanium was carried out to improve wear resistance using Laser Engineered Net Shaping (LENS™) — a commercial rapid prototyping technology. During the coating process a Nd:YAG laser was used to create small liquid metal pool on the surface of Ti substrate in to which SiC powder was injected to create Ti-SiC metal matrix composite layer. The composite layers were characterized using X-ray diffraction, scanning and transmission electron microscopy equipped with fine probe chemical analysis. Laser parameters were found to have strong influence on the dissolution of SiC, leading to the formation of TiSi₂, Ti₅Si₃ and TiC with a large amount of SiC on the surface. Detailed matrix microstructural analysis showed the formation of non-stoichiometric compounds and TiSi₂ in the matrix due to non-equilibrium rapid solidification during laser processing. The average Young's modulus of the composite coatings was found to be in the range of 602 and 757 GPa. Under dry sliding conditions, a considerable increase in wear resistance was observed, i.e., 5.91 × 10^− 4 mm³/Nm for the SiC reinforced coatings and 1.3 × 10⁻³ mm³/Nm for the Ti substrate at identical test conditions.     

Corrosion inhibitor systems for remedial treatment of reinforced concrete. Part 1: calcium nitrite

Laboratory investigations were performed to assess the efficacy of calcium nitrite as an inhibitor when used in surface treatments applied to reinforced concrete specimens that were chloride contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately 18 months thereafter. On completion of the exposure tests, measurements of corrosion weight losses and their distribution on the steel surfaces were also made. In non-carbonated specimens with high levels of internal chloride and carbonated specimens with even low levels of internal chloride, the surface-applied inhibitor treatment appeared to be ineffective under the conditions of the experiments and enhancement of local corrosion rates was observed in some specimens.     

Corrosion inhibitor systems for remedial treatment of reinforced concrete. Part 2: sodium monofluorophosphate

Sodium monofluorophosphate (MFP) has been applied in the form of concentrated aqueous solutions to the surfaces of concrete structures with the aim of inhibiting corrosion of embedded reinforcing steel which has become depassivated as a consequence of carbonation and/or chloride contamination. To evaluate the effectiveness of such treatments, a series of laboratory investigations was undertaken with reinforced concrete specimens that were chloride-contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately 18 months thereafter. Gravimetric measurements of the quantities and distribution of corrosion on the steel were also made on completion of the exposure tests. It has been found that there were no marked reductions in the corrosion rates of the steel under the conditions investigated. Analysis of aqueous extracts from the treated concrete specimens by means of ion chromatography revealed that negligible penetration of soluble MFP ions had occurred into any of the specimens. Hydrolysis products of MFP (phosphate and fluoride) were present at significant depths in aqueous extracts of the carbonated concrete specimens but only fluoride was detectable in similarly obtained aqueous extracts of non-carbonated specimens.     

Thermal analysis of laser surface transformation hardening—optimization of process parameters

This paper deals with the optimization of process parameters for maximum productivity (given by the product of scanning velocity and cross feed) in laser transformation hardening. The process parameters considered are laser beam power, P; laser beam diameter, D_b; and the heat intensity distribution, namely, normal, bimodal, or uniform. A thermal analysis of the laser surface transformation hardening of gears was conducted (based on Jaeger’s classical moving heat source method) by considering the laser beam as a moving plane (disc) heat source to establish the temperature rise distribution in the workpiece (gear) of finite width. In a recent investigation [Int. J. Heat Mass Transfer 44 (2001) 2845], the authors considered the case of a heat source with a pseudo-Gaussian (or normal) distribution of heat intensity. The analytical results were compared with the experimental results published in the literature. In laser heat treatment of steel, it is generally considered preferable to use a wider heat intensity distribution, such as uniform or bimodal, for it enables more uniform case hardening depth. In this paper, this model is extended to cover bimodal and uniform distributions and compared with the normal distribution. Scanning velocities for no surface melting and for a case hardening depth of 0.1 mm were determined for surface transformation hardening of AISI 1036 (EN 8) steel for a range of laser beam powers, P, laser beam diameters, D_b, and various heat intensity distributions. Since diffusion during the heat treatment (surface transformation hardening) process is a time dependent phenomenon, based on the literature review, an interaction time of 15 ms was taken as a basis. It is hoped that laser industry with adequate facilities available can validate the thermal analysis and subsequent optimization presented in this paper.