激光预加工对铝化物渗层低温成形工艺的影响

目的 研究K4169镍基高温合金表面激光熔凝预处理对铝化物渗层制备温度的影响。方法 先对镍基合金进行表面激光熔凝处理,分析表面熔凝层显微组织变化,再采用包埋渗法制备铝化物渗层,对比研究熔凝处理前后对渗层形成温度的影响。结果 经激光熔凝处理后,合金试样表层晶粒显著细化;预处理后的合金试样表面经900 ℃保温5 h所制备的渗层,与未处理的经1050 ℃保温5 h所制备的渗层具有相似的厚度及组织结构特征。结论 激光熔凝预处理可有效降低镍基合金表面铝化物渗层的成形温度,减轻渗层成形时高温长时处理对基体合金力学性能的影响。     

激光快速熔凝Fe基、Ni基合金的细化形态

采用脉冲激光对纯 Fe、纯 Ni、20钢和 Ni 基合金进行了快速熔凝处理。结果表明,在纯 Fe和纯 Ni 熔凝区内,生成了一种外延生长的晶粒组织;在20钢和 Ni 基合金熔凝区内,生成了外延生长晶粒和极细的枝晶组织。在金属与合金的熔区中均形成了精细的的亚晶粒。激光快速熔凝大大地细化了校晶和亚晶,却没有得到明显细化的晶粒。     

高碳高合金钢的激光表面熔凝处理的耐磨性研究

研究了激光表面熔凝处理前后的高碳高合金钢Cr12的耐磨性能，并结合激光熔凝后组织的转变。分析了耐磨性提高的原因。结果表明：咸度的提高，熔凝层中超细化的组织，大量的残余奥氏体使得激光处理后的材料的耐磨性能大幅度提高。     

钢表面激光熔覆Ni基ZrO2（4Y）陶瓷层的研究

本文用ＳＥＭ，ＥＤＡＸ，ＸＲＤ和显微硬度计分析了４５钢表面激光熔覆Ｎｉ基ＺｒＯ２（４Ｙ）陶瓷层的组织结构与性能。结果表明：激光熔覆的Ｎｉ基ＺｒＯ２（４Ｙ）陶瓷层出现分层现象，表层为致密的ＺｒＯ２陶瓷层，与钢基体结合的中间层为Ｎｉ基合金；陶瓷层主要由ｔ－ＺｒＯ２相与少量Ｎｉ基γ固溶体组成，激光的快速熔凝过程抑制了ＺｒＯ２的ｔ－ｍ相转变；在最优激光参数条件下，可获得与钢基结合良好的致密ＺｒＯ２陶瓷熔覆     

高铬钢激光熔凝处理后的组织与耐蚀性能

快速凝固技术是改善高铬钢表面性能的有效手段,其中激光熔凝处理最为简单经济.过去,对采用激光熔凝处理来提高材料耐蚀性的报道不多,为此,采用5 kW横流CO2激光器对高铬钢进行熔凝强化处理,借助电化学测试、扫描电镜等方法研究了高铬钢激光熔凝处理后的显微组织及耐蚀性能.结果表明:高铬钢的表面腐蚀始于碳化物与基体交界处,导致基体腐蚀严重,大量碳化物暴露于表面;激光熔凝处理明显改善了高铬钢的组织形态,使其晶粒细化,碳化物完全溶解,碳及合金元素固溶于奥氏体枝晶中,耐蚀性明显提高,腐蚀表面均匀平整.     

钛合金表面激光熔覆Ni基合金涂层中析出相热力学模拟计算

采用横流CO2激光器在TC4合金表面熔覆Ni基合金涂层,对激光熔覆层的微观组织、析出相、各合金元素在γ-Ni和M23C6相中含量变化进行了研究.结果表明,熔覆层可分为三个区:熔覆区、结合区和基体热影响区.熔覆区由γ-Ni,TiB2,TiC,M23C6和Ni3B相组成,其中,TiB2,TiC和M23C6细小颗粒均匀分布于γ-Ni初晶上,共晶组织由γ-Ni和Ni3B组成.为揭示TC4合金表面激光熔覆Ni基合金涂层在3500～500K温度范围的相组成及组织变化规律,利用Thermo-Calc软件及相应Ni基合金数据库对TC4合金表面激光熔覆Ni基合金涂层凝固过程中各析出相进行了热力学计算分析,研究了熔覆层中γ-Ni,TiB2,TiC,M23C6和Ni3B各相相对含量和B,C,Cr,Fe,Ni,Ti元素在γ-Ni和M23C6相中的含量随温度变化关系,为TC4合金表面激光熔覆Ni基合金涂层成分设计和工艺优化提供理论依据.     

轮轨试样Co基合金激光熔覆层组织及磨损性能

为提高轮轨材料的耐磨性降低轮轨磨损,利用CO2多模激光器在轮轨试样表面获得Co基合金熔覆层,测试分析了其组织结构性能和显微硬度,利用MMS-2A微机控制摩擦磨损试验机对比研究了激光熔覆处理与未处理轮轨试样的抗磨损性能.结果表明:激光熔覆处理后在轮轨试样表面获得与基体良好结合厚度约1 mm的熔覆层;熔覆层主要由枝晶(γ-Co)和共晶组织(Cr23C6+γ-Co)构成,初生相为γ-Co过饱和固溶体,富含Cr元素,共晶组织中富含Co元素;结合区为粗大柱状晶,从中部到表层出现胞状晶、树枝晶等多种形态.离界面越远组织越细密,组织生长方向紊乱;结合区存在元素扩散,尤其是Fe、Cr和Co含量变化显著;激光熔覆Co基合金后轮轨试样硬度分别提高约52.98%和43.44%,能有效降低对摩副磨损,轮轨抗磨损能力提高约为原来的5倍.     

GCr15轴承钢激光表面熔凝强化的研究

本文研究了 GCr15轴承钢经激光表面熔凝处理后显微组织的变化,讨论了激光表面熔凝的强化机理。激光表面熔凝强化的本质是马氏体的孪晶强化,残余奥氏体的形变强化、碳的固溶强化及枝晶细化强化等。     

稀土渗碳对GCr15钢激光熔凝层摩擦行为的作用

为了提高在航空航天和民用等领域中广泛使用的GCr15钢的表面强度及耐磨性能,采用激光熔凝方法对GCr15钢表面稀土渗碳层进行改性处理,研究了稀土渗碳对激光熔凝改性层摩擦系数及磨损量的影响.结果表明:稀土渗碳使GCr15钢表面激光熔凝改性层的摩擦系数有所下降且在整个摩擦过程中波动较小,磨损失重为未经改性处理的基体材料失重的14%(质量分数);随着摩擦时滑动距离的增加及载荷的加大,稀土渗碳激光熔凝改性处理降低磨损失重的作用也显著增大;稀土渗碳层的磨损形式为犁沟磨损,而稀土渗碳激光熔凝处理的改性层则属于局部擦伤型;稀土渗碳在钢表面激光熔凝处理中的作用主要表现为细化晶粒、微合金化、净化和改善组织致密性.     

轻质高温结构材料--γ-TiAl基合金的研究动向

γ-TiAl基合金被认为是非常有前途的新型轻质高温结构材料,在航空航天、汽车等领域具有广阔的应用前景.简要介绍了γ-TiAl基合金的研究概况,并从高铌合金化、复合化、纳米化等方面着重阐述了其今后的发展趋势.     

Superplastic diffusion bonding of γ-TiAl-based alloy

With laser surface melting and conventional heat treatment, superplastic diffusion bonding of TiAl alloy samples was carried out. Three different microstructure, i.e. fully lamellar structure, fine dendritic structure and refined equiaxed structure are used and their effects on bonding quality were investigated, and the bond quality was assessed by shear test at room temperature. Sound bonds could be achieved at 900 °C by laser surface modification or by laser surface modification and pre-bond heat treatment at 1000 °C for 60 min, which is lower than conventional diffusion bonding temperature. The bonds were also post-bond heat treated at 1200 °C for 30 min, which improved the bond quality in all cases. The best shear strength of the bonds is greater than 80% of that of base metal.     

Annealing-induced Grain Refinement in a Nanostructured Ferritic Steel

A nanostructured surface layer with a mean ferrite grain size of ～8 nm was produced on a Fe-9Cr steel by means of surface mechanical attrition treatment. Upon annealing, ferrite grains coarsen with increasing temperature and their sizes increase to ～40 nm at 973 K. Further increasing annealing temperature leads to an obvious reduction of ferrite grain sizes, to ～14 nm at 1173 K. The annealing-induced grain refinement is analyzed in terms of phase transformations in the nanostructured steel.     

Effect of grain refinement on strain hardening and fracture in austenitic stainless steel

The present study aims to investigate the effect of grain refinement on strain hardening behaviour and fracture surface characteristics in 316LN austenitic stainless steel (ASS). The ASSs with varying grain sizes were obtained through 90% cold rolled reduction and subsequently phase reversion annealing treatment. The results showed that the grain refinement from coarse-grained (CG) structure to ultrafine-grained (UFG) structure increased the yield strength whilst maintaining a reasonable ductility. The strain hardening curves in all the samples were divided into three stages. The fractures in all the samples were ductile fracture with dimples. The subtle differences in the strain hardening behaviour and fracture surface characteristics among the samples with various grain sizes from CG structure to UFG structure were influenced by the deformation mechanisms of austenite.     

EFFECT OF LASER SURFACE TREATMENT ON HIGH CYCLE FATIGUE OF AISI 316L STAINLESS STEEL

Abstract— The effect of a laser surface treatment on the high-cycle fatigue behaviour of the austenitic stainless steel AISI 316L was investigated. The specimens were subjected to a surface melting using a CO₂-laser. Although this treatment introduced tensile residual stresses in the melted and resolidified surface layer and intensified the surface roughness, the fatigue limit could be increased by 20% with respect to the as-received specimens. It is suggested that grain refinement in the rapidly resolidified surface layer is mainly responsible for this improvement.     

Effects of laser irradiation on the structure and optical properties of ZnO thin films

The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar⁺ laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500 °C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.     

超声振动辅助激光退火对FTO薄膜光电性能的影响

在激光退火处理掺氟二氧化锡(FTO)透明导电薄膜过程中引入超声振动, 研究了超声振动辅助激光退火对FTO薄膜晶体结构、表面形貌和光电性能的影响。结果表明: 与未施加超声振动时相比, 该方法可使薄膜上下位移而引起激光聚焦状态发生连续变化, 由此保证薄膜处于最佳退火范围内, 同时还可使薄膜表面激光熔融区域的颗粒被振动分散, 由此抑制颗粒团聚, 提高颗粒分布的均匀性和致密度, 最终有效地改善薄膜的光电性能。当振动功率为300 W时, 薄膜表面结构最为均匀、致密和平整, 此时光电性能达到最佳, 它在400~800 nm波段的平均透光率为84.7%, 方块电阻为9.0 Ω/□。     

Effects of Laser-Cutting and Spark Erosion Techniques and Heat Treatment on the Magnetic Properties of Grain-Oriented Transformer Steels

Spark erosion and laser-cutting processes were examined in terms of their effects on the magnetic properties of grain-oriented electrical steels at working frequencies. The maximum permeability value in each case was considered a reference to determine the quantitative effect of cutting and eroding methods as well as the effects of heat treatment. To minimize the deterioration that appears after the piercing process is implemented, the specimens were subjected to heat treatment at the most appropriate temperature. The influence of stress-relief annealing could be observed throughout the domain refinement on the surface by using magneto-optical Kerr microscopy. Additionally, it was clearly seen that the domain contrast at the cut edge of the spark-eroded sample was more uniform than that provided by laser cutting upon applying a high AC-field amplitude.     

Grain structure of laser remelted 7075 aluminium alloy in presence of Al2O3 particles

Abstract

The effect of inert particles on grain structure development from alloy melt during laser rapid solidification has been investigated. It is found that the presence of Al₂O₃ particles may disrupt the usual epitaxial grain structure evolution of an aluminium 7075 alloy when processed by laser surface remelting. This result, in addition to observations of crystal termination at the particles and grain refinement in particle dense regions, indicates that a mechanism of particle restricted grain growth operates.     

超声冲击处理2A12铝合金焊缝表层微观组织结构变化

采用超声冲击工艺对母材为2A12铝合金焊接接头进行了焊后处理.利用扫描电镜、X射线衍射分析了超声冲击处理前后焊缝表面层的微观组织结构特征.结果表明,超声冲击处理可以在焊缝表面形成约为300μm的致密塑性变形层,晶粒明显细化.对X射线衍射峰的观察分析表明,处理后焊缝表层材料衍射峰明显宽化,这是超声冲击处理使焊缝表层材料粒子细化和晶格结构的微观应变引起的.利用谢乐方程和威尔逊公式对超声冲击处理后焊缝表层的晶粒度和微观应变进行了定量分析,结果表明,处理层的晶粒平均尺度为123nm,平均微观应变为0.134%.最后,对晶粒细化的机理进行了分析.     

退火态激光选区熔化成形AlSi10Mg合金组织与力学性能

AlSi10Mg合金具有高比强度、高耐磨性等优良特点。由于其成分接近共晶点,成形性能良好,被广泛应用于激光选区熔化技术。然而其热处理制度仍然沿用传统铸态合金的热处理规范,影响了其性能的充分发挥。本工作采用激光选区熔化技术制备了AlSi10Mg合金,并研究了沉积态和后续热处理过程中组织演化规律及其对室温力学性能的影响机制。研究发现：沉积态组织由沿沉积方向生长的α-Al柱状枝晶及枝晶间网状Al-Si共晶组成,具有强烈的〈100〉方向织构,沉积层由三部分组成,分别是细晶区、粗晶区及热影响区,抗拉强度389.5 MPa,伸长率4%。退火过程中,共晶Si破碎、球化,基体中过饱和Si不断析出长大。当退火温度从200 ℃提高到500 ℃时,Si颗粒发生Ostwald熟化,平均尺寸增长了23倍。经过300 ℃和500 ℃退火处理后,试样抗拉强度分别为287.0 MPa和268.0 MPa,但伸长率分别提高到10.3%和17.2%。