激光微熔覆沉积工艺中TC4粉末精确喷射技术研究

在目前的激光熔覆沉积制造工艺中,送粉技术主要是利用气体大量送粉,粉末输送精度不高,导致熔覆过程中粉末的利用率低且制造精度不高。利用微流体数字化喷射技术来实现粉末的精确喷射,并利用搭建的激光微熔覆成形制造系统,研究了钛合金粉末单喷管和双喷管精确喷射时参数对喷射精度的影响,并进行了对比。利用单喷管送粉进行了单道熔覆实验,分析了激光功率、扫描速度、送粉率等工艺参数对成形工艺的影响。

激光微熔覆技术的发展及应用

基于激光的直写技术具有加工周期短、使用灵活、无需掩模、环境要求低等诸多优点,其在微电子等领域应用广泛。本文引入了一种新的激光直写技术—激光微熔覆技术,介绍了该技术的工艺过程及特点,并在此基础上集成制造了激光微熔覆设备。通过激光与物质的相互作用原理,理论分析了激光微熔覆电子浆料的成型机理。最后,举例说明该技术在微电子、光电子以及传感器领域的应用,并对该技术的发展趋势进行了初步预测,认为该技术在混合集成电路基板的加工、微型传感器和加热器的制造、平面无源电子器件和分立无源电子器件的研制以及生物芯片、电子封装等领域有好的发展前景。

激光微熔覆柔性布线预置层控制工艺研究

预置层厚度和均匀性是影响激光微熔覆布线质量的关键因素,本文通过对旋转法匀胶工艺的系统研究,得出了温度和溶剂含量对导电浆料粘度的影响规律,并得出了预置层厚度控制的经验公式,给出了使预置层厚度均匀的最佳匀胶工艺,为激光微熔覆柔性布线铺平了道路。

激光微熔覆中实时自动对焦控制系统设计

在激光微熔覆过程中,为了避免加工误差,利用图像处理技术,对USB摄像头反馈的图像数据进行清晰度评价,通过串口控制数控工作台升降,完成激光焦点的聚焦,保证激光焦点时刻作用于金属粉末的表面,保证加工效果。

基于微细笔和激光微熔覆的设备研制

为了进一步提高激光柔性布线的效率,本文根据微细笔直写和激光微细熔覆的特点和原理,设计并制造了相关设备,自主开发了激光直写柔性布线软件。应用表明,该设备大大提高了柔性布线的效率。

激光微熔覆沉积成形工艺参数对TC4钛合金沉积组织的影响

通过改变激光微熔覆沉积制造过程中的激光功率和扫描速度,研究了成形工艺参数对TC4合金组织和显微硬度的影响。结果表明:激光微熔覆沉积组织可以为贯穿整个熔覆层的外延生长的柱状晶,也可能下部晶粒延续着前一层的柱状晶生长,最上部为快速凝固的枝晶薄层。宏观上存在明暗2个组织区域,当P/V值小于40 W·s·mm^(-1)时,成形试样的显微组织顶部区域为明区,下部为暗区。2个区域的组织都为细长针状马氏体,明区组织更细密。同时,明区的硬度要比暗区高,并且随着激光功率的增加或扫描速度的减小,顶部明区的宽度增加,而明区和暗区的硬度都呈下降趋势。反之为暗区在上,明区在下。此时,明区的组织仍然是细针状的马氏体组织。暗区是由于发生了固溶时效处理,细针状马氏体组织粗化,同时暗区的硬度要高于明区的硬度。

激光微熔覆制备SnO_2气敏膜及其性能研究

以纳米氧化锡(SnO2)粉末为原料,有机溶剂为载体,配置了SnO2浆料,通过激光微熔覆技术在氧化铝基板上制备了SnO2气敏膜。采用X射线衍射(XRD)和场发射扫描式电子显微镜(FE-SEM)分析研究了激光功率对SnO2气敏膜微观结构和气敏特性的影响规律。实验表明,随着激光功率的升高,纳米SnO2的晶粒逐渐长大,气敏膜对乙醇气体的灵敏度逐渐降低;激光微熔覆制备的气敏膜对体积分数为2×10-3乙醇气体的灵敏度最高达到8.6,与传统丝网印刷工艺制备的气敏膜性能相当。

Microstructure and high temperature tribological behavior of laser cladding Ni60A alloys coatings on 45 steel substrate

The crack-free Ni60 A coating was fabricated on 45 steel substrate by laser cladding and the microstructure including solidification characteristics, phases constitution and phase distribution was systematically investigated. The high temperature friction and wear behavior of the cladding coating and substrate sliding against GCr15 ball under different loads was systematically evaluated. It was found that the coating has homogenous and fine microstructure consisting of γ（Ni） solid solution, a considerable amount of network Ni-Ni3 B eutectics, m^23C6 with the floret-shape structure and Cr B with the dark spot-shape structure uniformly distributing in interdendritic eutectics. The microhardness of the coating is about 2.6 times as much as that of the substrate. The coating produces higher friction values than the substrate under the same load condition, but the friction process on the coating keeps relatively stable. Wear rates of the coating are about 1/6.2 of that of the substrate under the higher load（300 g）. Wear mechanism of the substrate includes adhesion wear, abrasive wear, severe plastic deformation and oxidation wear, while that of the coating is merely a combination of mild abrasive wear and moderate oxidation wear.

Influence of heat treatment on microstructure and mechanical properties of FeCrNi coating produced by laser cladding

The FeCrNi alloy powders were used on the dovetail groove of FV520B steel to fabricate the multilayer laser cladding layers. The effects of heat treatment on the microstructure and mechanical properties of FeCrNi layers were investigated. The results showed that the heat treatment at the temperature ranged from 1073 to 1273 K refined the grains of the substrate materials and removed the soft zone of hardness between the fused zone (FZ) and base material (BM) effectively mainly due to a secondary quench of heat treatment. When the temperature of heat treatment was 1073 K, the maximum ultimate tensile strength (UTS) values of the laser cladding component were obtained. However, the heat treatment at high temperature had a bad effect on wear resistance of coatings at some extent.

Surface modification of TC4 Ti alloy by laser cladding with TiC+Ti powders

Laser surface cladding was applied on a TC4 Ti alloy to improve its surface properties. Mixed TiC and Ti powders with a TiC-to-Ti mass ratio of 1：3 were put onto the TC4 Ti alloy and subsequently treated by laser beam. The microstructure and composition modifications in the surfaee layer were carefully investigated by using SEM, EDX and XRD. Due to melting, liquid state mixing followed by rapid solidification and cooling, a layer with graded microstructures and compositions formed. The TiC powders were completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The inter-dendritic areas were filled with fine a＇ phase lamellae enrich in A1. Mainly due to the reduced TiC volume fraction with increasing depth, the hardness decreases with increasing depth in the laser clad layer with a maximum value of HV1400, about 4.5 times of the initial one.

Effect of high-speed laser cladding on microstructure and corrosion resistance of CoCrFeNiMo_(0.2) high-entropy alloy

In order to study the corrosion resistance of high-speed laser cladding(HLC) coating while improving production efficiency,a CoCrFeNiMo_(0.2)high-entropy alloy(HEA) coating was prepared by HLC.The optimized parameters of HLC are laser power of 880 W,scanning speed of 18 m/min,overlapping ratio of 60%,and powder feed speed of 3 r/min.Then,the surface roughness,microstructure,phase composition,element distribution,and electrochemical properties in 3.5 wt% NaCl solution of the coatings were analyzed,respectively.The local surface roughness of the CoCrFeNiMo_(0.2)HEA coating was found to be 15.53 μm.A distinct metallurgical bond could be observed between the coating and the substrate.Compared to the conventional laser cladding(CLC),the results of electrochemical tests showed that CoCrFeNiMo_(0.2)HEA coating exhibited a significant passivation.The corrosion current density of 5.4411 × 10^(-6)A·cm^(-2) and the corrosion potential of-0.7445 V for the HLC coating were calculated by the Tafel extrapolation method.The CLC coating’s corrosion current density and corrosion potential are 2.7083×10^(-5)A·cm^(-2) and-0.9685 V,respectively.The HLC coating shows a superior corrosion resistance,crucially due to the uniform and fine grains.Under various complex and harsh working conditions,this method can be widely used in the field of repairing and remanufacturing of corro sion-proof workpiece s.

Effects of TiB_2+TiC content on microstructure and wear resistance of Ni55-based composite coatings produced by plasma cladding

TiB2-TiC reinforced Ni55 matrix composite coatings were in-situ fabricated via plasma cladding on steels using Ti, B4C, and Ni55 as precursor materials at different proportions. Effects of TiB2+TiC content of ceramics phase on the microstructure and wear resistance were studied. The results showed that ceramic phases TiB2 and TiC were in-situ synthesized by plasma cladding, and the ceramic phase content significantly affected tribological performance and the wear mechanism of coatings under different loads. The composite ceramics protected coatings from further delamination wear by crack-resistance under a load of 30 N. Severe abrasive wear and adhesive wear were prevented when the load increased to 60 N because of the high hardness and strength of ceramic phases. Moreover, a compacted layer appeared on the wear surface of coatings with high content of ceramic phases, which effectively decreased the friction coefficient and wear rate. The TiB2-TiC composite ceramics significantly improved the wear performance of metal matrix composite coatings by different mechanisms under loads of 30 and 60 N.

Microstructure and mechanical properties of interface between laser cladded Hastelloy coating and steel substrate

In order to improve the corrosion resistance of carbon steel,Hastelloy coatings were prepared on E235steel substrate by ahigh power diode laser with laser scanning speeds of6and12mm/s,respectively.The interface between the coating and substratewas firstly exposed by dissolving off the substrate.Its microstructure,composition and mechanical properties were systemicallystudied.Special“edges”along the grain boundary were found at coating/substrate interface.These“edges”consisted of intergranularcorrosion area and real grain boundary.The interface of coating mainly displayed austenite structure ascribed to the rapidsolidification as well as the dilution of Ni during preparation.Additionally,Hastelloy coating and its interface prepared at the speedof12mm/s showed higher hardness than that prepared at the speed of6mm/s.Grain boundaries had higher friction coefficient thangrains at both coating/substrate interfaces.Moreover,the interface at higher laser scanning speed exhibited smaller grains,lowerdilution rates of Ni and Fe as well as a better tribological property.

Microstructure and performance of laser cladding TiB_2 and Nickel-coated graphite composite coating on stainless steel 9Cr18

The antiwear and antifriction coating, which contains TiB2 and Nickel-coated graphite, has been obtained on stainless steel 9Cr18 by laser cladding. The processing method, microstructure, interface, microhardness, tribological properties and the forming mechanisms of the coating are analyzed. Results show that the microstructure of the clad coating are mainly long plume-like primary phase sosoloid Ni-Fe which form the matrix framework, while the in-situ anomalous synthetical TiC grains and uhrafine TiB2 grains uniformly disperse among the framework. The hardness and wear resistance of the coating has been greatly improved, which can be attributed to the reinforcement mechanism of TiC, TiB2, FeC, Fe3C and Cr23 C6. etc. At the same time, the coating has friction-reducing ability.

Residual stress distribution in different depths of TiNi/Ti_2Ni-based laser clad coating prepared at different environmental temperatures

This study aimed to effectively reduce the cracking susceptibility of the laser clad coating by enhancing the environmental temperature during laser cladding,and reveal the residual stress distribution in different depths of the coating.The TiNi/Ti2Ni-based coatings were prepared on Ti6Al4V by laser cladding at different environmental temperatures of25,400,600and800°C.The changes in residual stress along the depth of the coatings were investigated in detail by the nanoindentation method.Results showed that the average residual stress of2.90GPa in the coating prepared at25°C was largest.With the increase in environmental temperature,the average residual stress was reduced to1.34GPa(400°C),0.70GPa(600°C)and0GPa(800°C).For all the coatings,the residual stress was increased with increasing the distance from the coating surface.Enhancing the environmental temperature can effectively reduce the cracking susceptibility of the coatings.

Microstructures and properties in surface layers of Mg-6Zn-1Ca magnesium alloy laser-clad with Al-Si powders

Laser surface cladding with Al-Si powders was applied to a Mg-6Zn-1Ca magnesium alloy to improve its surface properties.The microstructure,phase components and chemical compositions of the laser-clad layer were analyzed by using X-ray diffractometry(XRD),scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS).The results show that the clad layer mainly consists ofα-Mg,Mg2Si dendrites,Mg17Al12and Al3Mg2phases.Owing to the formation of Mg2Si,Mg17Al12and Al3Mg2intermetallic compounds in the melted region and grain refinement,the microhardness of the clad layer(HV0.025310)is about5times higher than that of the substrate(HV0.02554).Besides,corrosion tests in the NaCl(3.5%,mass fraction)water solution show that the corrosion potential is increased from-1574.6mV for the untreated sample to-128.7mV for the laser-clad sample,while the corrosion current density is reduced from170.1to6.7μA/cm2.These results reveal that improved corrosion resistance and increased hardness of the Mg-6Zn-1Ca alloy can be both achieved after laser cladding with Al-Si powders.

Microstructure and properties of WC-12Co composite coatings prepared by laser cladding

A comprehensive study of the phase composition, microstructure evolution, microhardness and wear performance of WC-12 Co composite coatings fabricated by laser cladding using coaxial powder-feed mode was presented. It was shown that a combination of high scan speed and high laser energy density made WC on the edge of WC-12 Co composite powders partially melt in liquid Co and 304 stainless steel matrix, and then new carbides consisting of lamellar WC and herringbone M3 W3 C(M=Fe,Co) were formed. Meanwhile, WC-12 Co composite coatings with no porosity, cracks and drawbacks like decarburization were obtained, showing high densification and good metallurgical bonding with the substrate. Furthermore, a considerably high microhardness of HV0.3 1500-1600, low coefficient of friction of 0.55 and wear rate of(2.15±0.31)×10-7 mm3/(N·m) were achieved owing to the synergistic effect of excellent metallurgical bonding and fine microstructures of composite coating under laser power of 1500 W.