激光镀技术

介绍了激光镀技术的概念,应用及意义,并着重对激光辅助电沉积,激光诱导化学镀,激光辅助化学气相沉积或激光辅助物理气相沉积三方面的应用及前景做了详细的介绍。     

激光法制备纳米材料的进展

对激光法制备纳米材料作了简要回顾,着重介绍了制备纳米粒子、纳米纤维、纳米薄膜的激光诱导气相沉积、激光消融等方法。     

激光化学气相沉积(LCVD)制取TiN薄膜

研究了在W18Cr4V高速钢基体上，用CO2连续激光诱导化学气相沉积TiN薄膜的工艺方法。激光功能600W，在H2、N2、TiCl4反应系统中沉积出TiN薄膜，薄膜的颜色呈金黄色，显微硬度为2500HV。     

模具钢表面连续激光沉积TiN类薄膜的研究

利用波长为10．6mm的CO2连续激光诱导化学气相沉积的方法，在模具钢基体上沉积TiN类薄膜。采用XRD、OM、SEM、EDS等手段分析薄膜的组织和相结构。结果表明，当激光功率为600W，扫描速度为2mlrffs。通过H2、N2和TiCl4之间的化学反应，在模具钢表面获得了均匀致密的枝晶组织，其显微硬度最高可达2500HV。     

模具钢表面连续激光沉积TiN类薄膜的研究

利用波长为10.6mm的CO2连续激光诱导化学气相沉积的方法,在模具钢基体上沉积TiN类薄膜。采用XRD、OM、SEM、EDS等手段分析薄膜的组织和相结构。结果表明,当激光功率为600W,扫描速度为2mm/s,通过H2、N2和TiCl4之间的化学反应,在模具钢表面获得了均匀致密的枝晶组织,其显微硬度最高可达2500HV。     

模具钢表面连续激光沉积TiN类薄膜的研究

利用波长为10．6gm的CO2连续激光诱导化学气相沉积的方法，在模具钢基体上沉积TiN类薄膜。采用XRD、OM、SEM、EDS等手段分析薄膜的组织和相结构。实验表明，当激光功率为600W，扫描速度为2mm／s，通过H2、N2和TiCl4之间的化学反应，在模具钢表面获得了均匀致密的枝晶组织，其显微硬度最高可达2500HV。     

模具钢表面连续激光沉积TiN类薄膜的研究

利用波长为10.6 μm的CO2连续激光诱导化学气相沉积的方法,在模具钢基体上沉积TiN类薄膜.采用XRD、OM、SEM、EDS等手段分析薄膜的组织和相结构.实验表明,当激光功率为600W,扫描速度为2 mm/s时,通过H2、N2和TiC14之间的化学反应,在模具钢表面获得了均匀致密的枝晶组织,其显微硬度最高可达2500HV.     

迅速崛起的激光表面处理技术

激光表面处理技术正在不断扩大其工业应用范围－激光表面相变硬化，包覆，熔化和合金化之类的表面处理工艺和来改善材料的表面性能。而了近的ＵＶ激光的进展拓开了这一技术的应用范围并增加了灵活性，这包括表面结构的改善，增加粘着和结合能力以及激光物理气相沉积，激光化学气相沉积等。此文扼要地阐述了这些工艺过程，可能的应用区域及其优点。     

一种激光化学气相沉积金刚石膜的方法（专利号：95111978．8）

一种激光化学气相沉积金刚石膜的方法，最低沉积温度为250℃，其特征在于选用波长在308nm的XeCl准分子激光作激光源，过程如下：将欲沉积衬底放在高导热率材料的工作台上，用XeCl准分子激光辐照衬底欲沉积金刚石膜区，并在预抽真空的反应室中通入能吸收该激光波长的碳氢化合物反应气(含汽化液体或固体)和氢气。     

用高能束流进行钛合金表面改性

概述了利用高能束流进行材料表面改性的技术及其对钛合金表面改性的应用。这些技术包括激光固态相变强化处理,激光表面熔凝处理、激光表面合金化、离子注入、离子束混合和离子束辅助气相沉积。钛合金经高能束流表面改性处理可以提高其表面硬度、耐磨性和耐腐蚀性能。     

An investigation of the synthesis of metallic nano-particles by laser ablation

A numerical model is proposed to simulate the deposition process of the metallic particles under laser irradiation, in order to investigate the formation mechanism of the nano-particles for the mass production. The deposition of nano-particles has been effectively made by a Q-switched laser irradiation of nickel substrate. In the analysis of the localized ablation phenomenon, which was induced by a high peak power laser, the deposition of nickel nano-particles with narrow size distribution has been examined. The analysis of fabrication mechanisms has been studied for the process design from the macroscopic to microscopic views and the process characteristics of the laser ablation for the nano-particle deposition has been verified experimentally and numerically.     

An investigation of energy loss mechanisms in water-jet assisted underwater laser cutting process using an analytical model

The water-jet assisted underwater laser cutting processes has relatively low overall efficiency compared to gas assisted laser cutting process due to high convective loss in water-jet from the hot melt layer and scattering loss of laser radiation by the water vapour formed at the laser–workpiece–water interaction region. However, the individual contribution of different losses and their dependency on process parameters are not fully investigated. Therefore, a lumped parameter analytical model for this cutting process has been formulated considering various laser–material–water interaction phenomena, different loss mechanisms and shear force provided by the water-jet, and has been used to predict various output parameters including the maximum cutting speed, cut front temperature, cut kerf and the loss of laser power through different mechanisms as functions of laser power and water-jet speed. The predictions of cutting speed, kerf-width and cut front temperature were validated with the experimental results. The modeling revealed that the scattering in water vapour is the dominant loss mechanism, causing ~40–50% of laser power loss. This also predicted that the percentage losses are lower for higher laser powers and lower water-jet speeds. In order to minimize the deleterious effect of vapour, dynamics of its formation due to laser heating and its removal by water-jet was experimentally studied. And, the cutting was done with modulated power laser beam of different pulse on- and off-times to determine the pulse on-time sufficiently short to disallow growth of vapour layer, still cutting be effected and the off-time enough long for water-jet to remove the vapour layer from the interaction zone before next pulse arrives. Compared to CW laser beam the modulated laser beam of same average power yielded higher process efficiency.     

Influence of a pulsed laser regime on surface finish induced by the direct metal deposition process on a Ti64 alloy

The direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allows generating a prototype or small series of near net-shape structures. Despite numerous advantages, one of the most critical issues of the technique is that produced pieces have a deleterious surface finish which requires post machining steps. Following recent investigations where the use of laser pulses instead of a continuous regime was successful to obtain smoother DMD structures, this paper relates investigations on the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titanium alloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate a specific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laser heating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsed mode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger and stable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients and Marangoni flow in the external side of the fusion zone were assumed to be the main reasons for surface finish improvement. Additional results indicate that combining the benefits from a pulsed regime and a uniform laser irradiation does not provide further reduction of surface roughness.     

激光化学气相沉积(连载之二)

介绍了激光化学气相沉积的基本原理,较详细地讲述了制备金属薄膜、金刚石薄膜、类金刚石薄膜、氢化非晶硅薄膜、化合物半导体薄膜及绝缘体薄膜等所用的激光器、工艺参数以及薄膜的性能.     

激光化学气相沉积(连载之一)

本讲座介绍了激光化学气相沉积的基本原理,较详细地讲述了制备金属薄膜、金刚石薄膜、类金刚石薄膜、氢化非晶硅薄膜、化合物半导体薄膜及绝缘体薄膜等所用的激光器、工艺参数以及薄膜的性能.     

激光化学气相沉积(连载之三)

本讲座介绍了激光化学气相沉积的基本原理,较详细地讲述了制备金属薄膜、金刚石薄膜、类金刚石薄膜、氢化非晶硅薄膜、化合物半导体薄膜及绝缘体薄膜等所用的激光器、工艺参数以及薄膜的性能.     

Phase change problem and effects of geometrical constants on weld pool geometry in sheet metal laser welding

Abstract

A three-dimensional quasi-state heat conduction model is presented for the solid/liquid interface in laser welding of thin sheet metals. The vapour plasma plume effect is incorporated into the model by considering the electromagnetic field equation to determine the laser power reaching the substrate surface after passing through the plume region. Optical properties, such as the dielectric constant and electrical conductivity of plume, and the thermal conductivity of the vapour of stainless steel 316 in the plume region are estimated. Elliptic-paraboloid weld pool geometry is considered and analytic expressions for temperature distributions are obtained in the solidand liquidregions based on theweld pool geometry. Experimental and theoretical results for the weld depths and widths areillustratedfor process parameters such as the laser power, welding speed, and weld pool shape factors in x and y directions.     

Diameter sensitive effect in singlewalled carbon nanotubes upon acid treatment

Singlewalled carbon nanotubes (SWCNT) exhibit very unique properties. As an electronic system they undergo amphoteric doping effects (n-type and p-type) which can be reversed. These processes affect the optical and vibronic properties of the carbon nanotubes. The most common and widely used procedure which changes the properties of the SWCNT is acid treatment applied as a purification procedure. This effect has been widely studied but not fully understood so far. Here, we present a study, in which a diameter sensitive effect has been observed. Therefore, two kinds of SWCNT samples have been studied: (i) produced via chemical vapour deposition with a broad diameter distribution, and (ii) synthesised by the laser ablation technique which is commonly known to result in narrow diameter distribution bulk SWCNT samples. Resonance Raman spectroscopy, optical absorption spectroscopy, and Fourier transform middle-infrared spectroscopy have been applied for the characterisation of the samples.     

Effects of Powder Geometry and Composition in Coaxial Laser Deposition of 316L Steel for Rapid Prototyping

Multiple layer laser powder deposition has recently been applied to producing fully dense 3-D metallic engineering parts for rapid prototyping and tooling. To date, however, the process has been limited to using only gas-atomised, spherical powders. In this paper, the feasibility of using water-atomised powders is investigated, based on an experimental comparison of gas- and water- atomised powders in multiple layer, laser fused deposition of 316L stainless steel. The work shows that, despite much lower cost (approximately 25% of the pries of gas-atomised powders), the water-atomised, irregular powders have superior deposition quality in terms of surface finish, deposition uniformity, microstructures and bonding between layers, compared to the gas-atomised powders under the same processing conditions, although deposition rate is lower. Powder geometry and oxygen content differences of the two powders have been found to be the principal reasons for the observed effects. Theoretical analyses of the beam-material interaction processes and malt pool behaviour are presented to explain the observed phenomena. The results indicate that there are both functional and economic reasons for using water-atomised powders for this additive manufacturing application.     

退火处理及沉积方向对激光沉积TA15钛合金性能和组织的影响

以TA15钛合金粉末为原料,利用激光沉积制造方法制备TA15钛合金拉伸试样厚壁件。通过光学显微镜(OM)、扫描电子显微镜(SEM)和X射线衍射(XRD)等方法研究退火温度及沉积方向对TA15钛合金组织、拉伸性能的影响,以及α相变形机制。结果表明：随着退火温度升高,显微组织中α相长宽比呈上升趋势;激光沉积成形TA15钛合金厚壁件在沉积和垂直沉积方向上的力学性能存在差异,沉积方向上的抗拉强度明显均低于垂直沉积方向上的抗拉强度;柱状晶晶界对α片层的受力变形有一定的阻碍作用;α片层通过挤压变形和滑移变形两种机制发生变形或断裂;两种方向上拉伸断裂方式不同,沿沉积方向上断裂为韧性断裂,沿垂直沉积方向上断裂为半解理半韧性断裂。