Substrate Strengthening of CVD Coated Steels

CHEMICAL VAPOR DEPOSITION is successfullyused in production since decades to enhance the wearresistance of tools.Excellent coating properties areachieved with relatively simple equipment.The highdeposition temperatures used for CVD favor a goodadhesion of CVD coatings on the substrate,but alsonegatively influence the properties of the steelsubstrates.High coating temperatures followed byrelatively low cooling rates demand a subsequent heattreatment to restore the properties of the s…     

Laser treatment and PVD TiN coating of Ti-6Al-4V alloy

Improved adhesion between a coating and the base substrate is necessary for successful engineering applications. This may be achieved through generating intermediate zone between the coating and the substrate. In the present study, laser gas alloying of Ti-6Al-4V alloy was carried out. Nitrogen was introduced co-axially with the laser beam while the workpiece is scanned at a constant speed in the x-direction during the laser heating process. The laser-treated workpieces were then slightly ground and TiN PVD coated. Thickness of the coating layer was limited to 2 μm. The wear tests were conducted on the laser-treated TiN-coated workpieces. To examine the metallurgical changes, microphotographs of workpiece cross-sections were taken. To monitor the nitride compounds in the surface region, XRD was carried out. It was found that three wear stages occur. The steady wear stage is relatively longer for laser-treated TiN-coated workpiece compared to the TiN-coated workpiece.     

Phase constituents and mechanical properties of laser in-situ synthesized TiCN/TiN composite coating on Ti-6Al-4V

Laser in-situ synthesis technology at room temperature was applied to obtain TiCN/TiN composite coating. A pulsed Nd:YAG laser (wavelength 1064 nm) was used to melt the mixture of Ti and C powder. Pure nitrogen gas with a pressure of 0.4 MPa was introduced coaxially together with laser beam to the melting pool to react with Ti and C atoms and in-situ synthesize TiCN/TiN composite coating. The coating consists of TiC_0.3N_0.7, TiN and TiN_0.3, but the proportions of these three constituents vary with the laser power density. SEM results revealed that dendrites were oriented in accordance with the heat flow and a metallurgical bonding between the coating and the substrate was achieved. The in-situ synthesized TiCN/TiN composite coating, with a thickness of about 200 μm, increased the hardness and wear resistance compared to the bare Ti-6Al-4V substrate. A remarkable improvement of the average microhardness (3-4 times) and an enhancement of the wear resistance (10-11 times) are observed by laser in-situ synthesizing TiCN/TiN composite coating.     

工模具钢表面化学气相沉积法强化技术应用研究

在实验和理论分析的基础上,利用化学气相沉积技术在工具钢和模具钢基体表面沉积TiN薄膜,以提高模具表面强度和耐磨性.     

微合金化对渗碳齿轮钢热处理畸变的影响

利用C形缺口试样,研究Nb-B微合金化齿轮钢的渗碳热处理畸变。结果表明,由于细小的Nb（C,N）析出相在奥氏体晶界起钉扎作用,Nb-B微合金化渗碳齿轮钢的原奥氏体晶粒平均尺寸明显细于20CrMoH钢和22CrMoH钢。微量B使20CrMoH钢和22CrMoH钢的淬透性提高,理想淬透直径DI值增大,渗碳淬火畸变率增加;Nb微合金化细化晶粒,细晶粒齿轮钢的渗碳淬火畸变相对较小;Nb-B微合金化可实现淬透性提高而渗碳淬火畸变不显著增加。     

Process planning for laser-assisted forming

Laser forming has emerged as a viable means of assisting conventional forming processes with geometrical accuracy-related problems. By combining the incremental nature of laser forming with conventional processes such as brakeforming which forms material by a single continuous movement of the tooling, the exact specified bend angle and radius of curvature of the bent component may be approached. This may be achieved by sequential or simultaneous application of the conventional tooling and the laser beam. The laser beam may be applied once to the forming zone or multiple laser beam scans may be used.

The combined process allows the forming of highly accurate sheet metal products in a cost effective way, through the possibility to make corrections to the bend angle in a controlled way. Furthermore, the combined process makes it possible to form intricate products that cannot be bent on a press brake due to collision problems or problems emanating from spring-back.

Consequently there are new implications for process planning in brakeforming when a laser beam is used in combination. These implications are discussed for some primitive applications.     

Finite-element simulation of moving induction heat treatment

An efficient finite-element procedure with a remesh scheme has been developed for the analysis of the moving induction heat treatment process, wherein relative motion occurs between the coil and the workpiece. In this procedure, the magnetic field is first simulated by using an updated mesh that tracks the moving coil position; the moving heat source within the workpiece material is derived from the magnetic field. The heat equation is then solved to obtain the temperature field created by the heat source. The procedure has been applied to calculate the temperature distributions in 1080 carbon steel cylinders during induction heating. The calculations have been validated by comparison with analytical solutions for the temperature distribution obtained using Green’s function methods. Finally, the temperature, residual stress, and microstructure distributions in quenched 1080 steel cylinders have been obtained using the finite-element procedure. Quenching of the heated cylinders, by both a moving cooling ring and a stationary liquid bath, has been analyzed. The finite-element procedure presented incorporates temperature-dependent material properties, phase transformations occurring in the 1080 steel, the change in magnetic permeability of the 1080 steel at the Curie temperature, and an elastoplastic stress model based on a mixed hardening rule. The simulation results demonstrate that the finite-element procedure could be applied to a variety of moving induction heat treatment problems to determine the residual stress and microstructure distributions in the heat-treated component. It also could be used in the design of process parameters and coils.     

Laser transformation hardening of carbon steel sheets using a heat sink

A heat-sink assisted laser transformation hardening method is presented as a way to enhance the hardenability of carbon steel sheets. In this study, the thermal conductivity of the heat sink and the thermal contact resistance between the steel sheet and the heat sink were identified as the two primary parameters for the process. Using a process map approach, the heat-treatability of steel sheets was studied theoretically focusing on carbon diffusion and cooling time characteristics. For validation purposes, 2 mm thick DP 590 and boron steel sheets were laser-hardened using four types of heat sink: stainless steel, steel, copper, and no heat sink. Surface hardness, hardening width and depth were measured and analyzed over a wide range of process parameters. From this study, it was revealed that, when a heat sink is used, both cooling and carbon diffusion characteristics become roughly on par with those of the thick plate case, but the heat treatable region remains similar to that of the no heat sink case. The use of a heat sink was found to be an effective way of enhancing the hardenability of steel sheets and the amount of enhancement is largely proportional to the heat sink thermal conductivity.     

Thermal processes in solidification of particles of a coating in plasma spraying

The laser welding methods of corrosion-resistant steel, aluminium and magnesium alloys, titanium, cast iron, dissimilar and other materials are examined. These methods are used in automobile, medical, electronic, shipbuilding and other industries.     

热处理对15CrMnMoVA钢力学性能的影响

为了得到无缝钢管实用的热处理工艺,将15CrMnMoVA钢棒料在不同淬火介质中淬火后不同温度回火;以及将15CrMnMoVA无缝钢管在真空炉中风淬至室温,然后在不同温度下回火.对其回火后的力学性能进行了检测.结果表明,棒料和无缝钢管在500～ 650℃回火后强度、硬度均会增加.XRD分析表明回火中产生的合金碳化物Mo2C和VC是强度、硬度增加的原因.考虑到尺寸精度在实际应用中的严格要求,推荐真空炉风淬后625 ℃回火为这种无缝钢管的热处理工艺.     

激光热处理发展现状

报导了国内、外激光热处理设备、工艺、理论研究的概况；并重点概述了激光热处理工业应用和产业化发展的现状及市场动态。     

Predictive modeling of laser hardening of AISI5150H steels

This paper presents accurate predictive modeling of the laser hardening process in terms of laser operating parameters and initial microstructure without the need of any experimental data. The model provides the diagrams that are useful for predicting hardness profiles, optimizing practical process parameters and assessing the potential of laser hardening for different steels. It is shown that the hardness and depth of the hardened layer in hypoeutectoid steels (carbon wt%<1) could be predicted from this model with good accuracy.The model combines a three-dimensional transient numerical solution for a rotating cylinder undergoing laser heating by a translating laser beam with a kinetic model describing pearlite dissolution, carbon redistribution in austenite and subsequent transformation to martensite by utilizing the feedback from the CCT diagram. In order to validate the thermal model and assert the accuracy of temperature predictions the temperature was measured using an infrared camera and a good agreement between the predicted and measured temperatures is shown. Results are presented as processing maps, which show how the case depth and hardness depend on input operating parameters. The good agreement between the measured and predicted hardness profiles ascertains the accuracy of the thermal-kinetic model developed for AISI5150H steels.     

高速钢工件表面物理化学气相沉积TiN

介绍了等离子化学气相沉积氮化钛技术在高速钢刀具和飞机用高速钢精密轴承上的应用，经ＰＣＶＤ－ＴｉＮ处理的高速钢刀具可以提高其表面强度，降低摩擦系数，从而提高其使用寿命，处理过的高速钢轴承精度高，具有抗高温氧化和抗热震性能，满足了使用要求。     

热处理对TiAlCN涂层组织和性能的影响

在Ar气条件下,对反应磁控溅射法制备的TiAlCN涂层进行500~1100℃热处理。采用XRD、Raman和DSC,研究不同热处理温度下涂层微观结构的变化,利用显微硬度计和划痕仪研究热处理对涂层性能的影响。结果表明,经600~800℃热处理后,涂层非晶碳相明显增加,使涂层形成纳米复合结构,这导致显微硬度显著增加,膜基结合性能增加;在900~1100℃热处理后,由于涂层中六方AlN相的析出,导致涂层显微硬度急剧下降,且韧性下降。     

热处理工艺对CLAM钢电子束焊缝显微组织与冲击韧性的影响

对聚变堆用中国低活化马氏体钢（CLAM钢）进行了真空电子束焊接试验,并对接头进行了回火和调质处理．利用光学显微镜（OM）、扫描电镜（SEM）及透射电镜（TEM）对焊缝热处理前后的显微组织进行了观察,并对焊缝进行了室温冲击试验．结果表明,焊态下,焊缝由粗大板条马氏体和δ铁素体构成,其冲击韧性较差;回火处理后,马氏体组织转变为回火马氏体组织,δ铁素体保存下来,且其晶界聚集了大量M23C6型碳化物．碳化物地聚集使得δ铁素体与原奥氏体晶界的结合减弱,在受到外部载荷作用时,裂纹易于萌生和扩展,故回火后焊缝冲击韧性未得到改善;调质处理消除了δ铁素体,焊缝组织转变为和母材相同的回火马氏体组织,焊缝冲击韧性显著提高．     

反应等离子喷涂TiN涂层热处理后的电化学腐蚀性能

研究了热处理后TiN涂层在模拟海水中的腐蚀行为,采用电化学阻抗谱(EIS)、动电位极化曲线、扫描电镜和能谱分析等技术研究了热处理后TiN涂层电化学腐蚀参数及组织的变化。结果表明:热处理后TiN涂层的耐蚀性明显提高,自腐蚀电流仅为热处理前的13.3%,极化电阻约是热处理前的20倍;电化学阻抗谱描绘了热处理后涂层的腐蚀过程及导致涂层腐蚀的主要因素,涂层局部的孔隙腐蚀是引起电化学腐蚀参数变化的主要因素,腐蚀初期孔隙电阻由大变小,后期又会由小变大,从而使涂层的腐蚀速率发生变化;热处理会使涂层的通孔率降低为87%,主要原因是在热处理过程,TiN与大气中的O2发生了氧化反应,生成密度较TiN小的TiO2相和Ti3O相,使涂层中的部分通孔被封闭,耐蚀性得以提高。     

Optimization of heat treatment in cold-drawn 6063 aluminium tubes

The effect of heat treatment condition on mechanical properties and bendability of 6063 aluminium cold-drawn tubes was investigated. The standardized heat treatment presently used in manufacturing of cold-drawn tubes increases the cost and time of the process which ultimately reduces plant productivity. The effects of time, temperature, and furnace heating rate were studied in order to identify an optimized heat treatment for tubes with different cold work levels. Drawn from the as-extruded state, tubes were heat treated to under-aged, peak-aged, and over-aged conditions with time and temperature ranging from 1 min to 24 h and 130–200 °C, respectively. Mechanical properties were determined with full section tensile tests whereas tube bendability was evaluated on an industrial draw bending machine. These characteristics were evaluated in each condition in order to identify the heat treatment which allows conforming to 6063-T832 temper requirements and gives sufficient bendability. Moreover, bendability was successfully correlated to fracture strain measured during a uniaxial tensile test and a threshold value over which problem-free bending operation was determined.     

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.     

离子束增强沉积工艺对镀层表面粗糙度的影响

研究了不同界面共混工艺对精密轴承镀层表面粗糙度的影响。结果表明 ,用氮离子进行界面反冲共混 ,在动态反冲共混过程中 ,随着氮离子能量的增高 ,氮离子选择溅射和界面碳富集造成界面上沉积的镀层表面粗糙度相应增大 ,而对于在工件表面预先沉积一层纯钛的静态反冲共混工艺 ,镀层具有较低的表面粗糙度。当氮离子能量为 40keV时 ,静态反冲共混界面具有高的镀膜基体结合力。