Titanium alloys after surface gas nitriding

Experimental studies using differential scanning calorimetry (DSC) for nitriding of four titanium-alloys near α Ti-8Al-1Mo-1V, near α Ti-6Al-2Sn-4Zr-2Mo, α + β Ti-6Al-4V and near β Ti-10V-2Fe-3Al at different temperatures and for different periods of time are presented. The X-ray diffraction (XRD) technique was used in order to study the phase transformations that occur during gas nitriding. As a result of the nitrogen interaction, a nitrided layer was formed that consists of titanium nitrides, followed by an interstitial solution of nitrogen in the hcp α titanium phase. The microstructural changes of these alloys in relation to the alloy composition and processing parameters were studied. It was found that the microstructure of alloys nitrided at temperatures below their β transus temperatures for various periods of time is uniform and homogeneous. With the increase of the temperature above their β transus temperatures the microstructure changes to irregular. Microindentation hardness testing using a Knoop indenter was conducted on the nitrided titanium alloys to analyse their hardness evolution in relation to the nitriding processing parameters and alloy composition. It was found that the microhardness increases with the increase of the temperature and time of nitriding. The surface morphology of the Ti-6Al-2Sn-4Zr-2Mo alloy in relation to the nitriding processing parameters was analysed.     

Relation Between the Microstructure and Properties of Commercial Titanium Alloys and the Parameters of Gas Nitriding

Titanium alloys are unique materials with an excellent combination of properties. However, their applications are limited due to low surface hardness. In the present work gas nitriding is performed with the aim of improving the surface properties of commercial titanium alloys. Four widely used titanium alloys, namely, Ti – 6% Al – 4% V, Ti – 6% Al – 2% Sn – 4% Zr – 2% Mo, Ti – 8% Al – 1% Mo – 1% V, and Ti – 10% V – 3% Fe – 3% Al, are studied. The process is performed in a nitrogen atmosphere at 950 and 1050°C for 1, 3, and 5 h. The resulting surface hardness exceeds the normal value for titanium alloys by a factor of 3 – 5 due to the change in the phase composition of the surface layer, yielding a solid solution of nitrogen in an α-Ti phase, a TiN nitride, and TiO₂ dioxide. The influence of the parameters of the treatment process and the chemical composition of the alloys on the phase composition, microstructure, microhardness, and thickness of the surface layer is analyzed. It is shown that nitriding of alloys with α- and (α + β)-structures at 1050°C yields surface layers with inhomogeneous composition and irregular thickness, whereas after nitriding at 950°C the surface layers are homogeneous and have high properties. Practical recommendations are given for choosing nitriding parameters for different alloys and variants of application are discussed.     

工业纯钛TA2激光气体氮化表面硬度的研究

激光气体氮化可以有效地提高钛合金表面硬度，从而改善钛合金耐磨损性能。通过金相组织观察和硬度测试分析了钛合金激光气体氮化时．激光气体氮化参量和激光光束分布对钛合金氮化后表面硬度的影响。结果表明，氮化区域内生成硬质相TiN是TA2钛合金表面硬度得到提高的主要原因，有利于硬质相TiN形成的激光气体氮化参量都会提高钛合金表面的硬度。而采用带式积分镜进行激光光束变换可以有效提高激光氮化处理的效率，钛合金平均表面硬度是原来的1.3倍。     

钛及钛合金的激光表面处理研究进展

激光表面处理是改善材料硬度、耐磨性和抗蚀性的有效途径。对钛及钛合金激光表面处理(激光表面合金化、激光熔覆和激光表面熔化)因可拓展其应用领域而备受关注。本文结合近年来的研究报道,全面综述2种激光表面处理即激光表面气体氮化和激光粉末合金化的影响因素,激光表面处理后表层组织、性能、缺陷控制以及激光参数的优化。在此基础上,阐述了目前存在的问题和今后的发展方向。     

Effect of the pressure in the gas-discharge chamber on the depth of nitrogen diffusion in titanium alloys

Among all the kinds of surface hardening of titanium alloys ion nitriding in a hydrogen-free medium is the most efficient and environmentally safe. The time of nitrogen saturation of titanium alloys by this method is 10–15 times shorter than in conventional nitriding. The acceleration of the diffusion of nitrogen under conditions of a glow discharge makes it possible to conduct the nitriding of (α+β)-titanium alloys at low temperatures that correspond to those of their aging, which had been impossible earlier. Diffusion saturation in ion surface impregnation is a multifactor process, which makes it controllable. One of the main controlling factors of ion nitriding is the pressure of the working gas. A study of the effect of the pressure in the gas-discharge chamber on the depth of nitrogen diffusion in titanium alloys (under conditions of stable existence of the glow discharge) made it possible to determine the dependence of the thickness of the layer and the specific power of the discharge on the nitrogen pressure and to determine the interrelation between the specific power and the saturating capacity of the gas medium. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 32–35, September, 1998.     

TC4激光气体渗氮层及其耐腐蚀性能

采用激光气体渗氮工艺可以在TC4钛合金表面生成一层高硬度、高耐磨性的氮化层。主要分析了激光气体渗氮后试样表面宏观状态的变化、渗氮层组织以及渗氮层耐腐蚀性能的变化。通过激光气体渗氮处理后,试样表面粗糙度增加;渗氮层自腐蚀电位相对于TC4钛合金的自腐蚀电位正移了0.042 4 V,表面耐腐蚀性能增强。     

Ti13Nb13Zr 合金离子氮化层的摩擦磨损性能研究

目的提高医用钛合金的耐磨损性能。方法应用等离子渗氮技术在Ti13Nb13Zr基材上制备改性层,并对改性层组织、成分及硬度进行测试。利用往复磨损试验机研究改性层在干摩擦条件下的摩擦磨损性能,并与未处理的基材进行对比。结果 Ti13Nb13Zr合金表面经渗氮后形成致密均匀的改性层,硬度高达1110HV0.025,改性层的磨损体积约为基材的1/23。结论等离子渗氮技术有效地改善了Ti13Nb13Zr合金的摩擦磨损性能。     

不同压力对 TC4 钛合金真空脉冲渗氮的影响

目的采用不同压力对TC4钛合金进行真空脉冲渗氮处理,提高其表面硬度及耐磨性。方法通过金相显微镜、X射线衍射仪、显微硬度计及耐磨试验机分析渗氮硬化层的组织与性能。结果 TC4钛合金经过真空气体渗氮处理后,形成了由Ti N,Ti2Al N和钛铝金属间化合物Ti3Al组成的复合改性层。渗氮压力太低,表面氮化物数量较少,氮化物层较薄;随渗氮压力的增大,表面氮化物数量增多,表面硬度及耐磨性增加。压力为0.015 MPa时,氮化物层表面硬度最大,表面硬度为1100~1200HV,有效硬化层深度为50~60μm。渗氮压力继续增加,表层组织变得疏松,表面硬度及耐磨性开始降低。结论选择合适的渗氮压力和表面氮浓度进行真空脉冲渗氮,可以提高钛合金表面硬度,改善耐磨性。     

纳米压/划痕表征激光渗氮层的弹塑性力学性能

利用脉冲式Nd：YAG激光在Ti6Al4V合金表面进行激光渗氮处理,借助纳米压痕和划痕试验表征渗氮层的弹塑性力学性能。结果表明,在钛合金表面成功制备了高硬度、高强度、枝晶状分布的渗氮层。同时,渗氮层内硬度、模量、强度以及应力-应变关系、摩擦系数等力学性能呈现出类似于激光渗氮层内氮元素扩散曲线的非均匀性空间分布规律。硬度和弹性模量之比以及纳米划痕试验结果表明,激光渗氮层的抗磨损性能随深度的增加逐渐降低,摩擦系数随着划入深度的增加,从0.2增加到0.4。     

Progress in control of nitriding potential in ASPN process

Abstract

A novel active screen plasma nitriding (ASPN) process provided excellent temperature homogeneity in the load and showed further progress in the control of nitriding potential. In addition to a variation of the nitrogen partial pressure in the process gas commonly used in the conventional plasma nitriding, the applied bias power strongly impacted the nitriding results. In the present work, an application of both methods for the control of nitriding potential in the ASPN process was systematically investigated for a wide range of process parameters to meet the treatment requirements for different types of engineering steel. A two-stage technique based on proper choice of process temperature and required nitriding potential in each stage has been applied in the ASPN process to avoid unnecessary compromises between sufficient thickness of the compound layer, the maximum case hardness and the acceptable nitriding hardness depth.     

TC4钛合金不同气源激光渗氮行为

在用矩形光斑高功率半导体激光器,在纯氮气和氮氩混合两种不同方式下,通过不同气流量和氮氩混合对Ti-6Al-4V进行表面渗氮,研究气体流量、氮氩混气比对渗氮熔池形态及渗氮组织和力学性能的影响。采用SEM、EDS以及XRD对渗氮层的显微组织、微区成分及相组成进行研究。结果表明:采用纯氮渗氮时,在15 L/min气流量下获得均匀渗氮层,继续增大气流量渗氮熔池流动紊乱,出现贯穿裂纹,且渗氮深度和硬度并未随气流量增加;采用不同氮氩混气比渗氮时,渗氮层的表层硬度均较相同条件下纯氮气渗氮层的有所降低,且渗氮层裂纹倾向减弱,渗氮层组织由表至里在200～800μm内按层深依次存在Ti N_0.88、Ti N_0.61、Ti N_0.3三种稳定相;分别采用纯氮气和不同氮氩混气比渗氮时,渗氮层组织沿层深分布依次均为粗短树枝晶、等轴晶、细长树枝晶、针状晶。     

TiAl基合金的辉光离子碳氮共渗研究

对TiAl基合金辉光离子碳氮共渗层组织与硬度进行了分析，结果表明，TiAl基合金经过碳氟共渗后可在表面形成碳、氮化合物的复合相结构，在金相显微镜下观察为灰暗色。随着共渗温度的升高和时间的延长，表层硬度逐渐提高。因此，TiAl基合金经过辉光离子碳氮共渗可达到既提高抗高温氧化性．又提高耐磨性的双重效果。     

Phase and structural changes in nitriding of iron alloyed with titanium

Conclusions Surface hardening of Fe–Ti alloys by nitriding is best with a titanium content not exceeding 1.3–1.5%. This produces a case with a high microhardness and good adhesion to the base metal. In alloys with a higher titanium content the amount of nitrogen dissolved in nitriding results in a sharp increase of the volume, embrittling the case and causing cracks.Kiev Polytechnical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 40–42, August, 1971.     

不同氮氩比对TC4合金激光气体渗氮的影响

针对TC4激光渗氮时产生裂纹而影响材料使用性能的问题,试验采用氩气和氮气的混合气体,对钛合金板块TC4进行激光气体渗氮,并研究了不同的氮气含量对渗氮层的裂纹、组织特征以及硬度等的影响.结果表明,在氮气含量低于40％的情况下,渗氮表面基本无裂纹产生;渗氮层的表面硬度以及渗氮深度随着氮气含量的降低而有所降低.另外还对渗氮层进行线扫描分析发现,在钛合金TC4激光气体渗氮过程中,渗氮层中的合金元素发生了选择性汽化现象.     

The interaction of titanium and titanium alloys with nitrogen at elevated temperatures. II. The nitridation behavior of alloys containing 5 weight percent of aluminum or chromium

The nitridation behavior of a Ti-5Al and a Ti-5Cr alloy has been examined at 1000°C and compared with the performance of pure titanium, involving gravimetric, metallographic, and microhardness studies. All of the materials corrode in accordance with a parabolic overall weight gain-time regime, pure titanium nitriding faster than either of the alloys. The reduced rates of nitridation of the alloys relative to pure titanium are reflected in the smaller relative depths of nitrogen dissolution in the substrates and may be accounted for by the corresponding decreased diffusivity values for nitrogen. The addition elements appear to play no part in the linear scaling reactions.     

Low temperature nitriding of AISI 316L stainless steel and titanium in a low pressure arc discharge

AISI 316L stainless steel (SS) and titanium nitriding were studied in a low pressure arc-assisted nitriding process where the substrate temperature and the plasma parameters are uncoupled. Lower nitriding temperature limits were explored for constant plasma parameters in Ar–N₂ gas mixtures and substrates at floating potential. Nitrogen superficial concentration, layer thicknesses and X-ray diffraction analyses were performed on SS specimens nitrided at two temperatures (580 and 680 K) for different times and titanium nitriding was studied in the temperature range 750–1025 K. At low temperature, the nitriding performances are limited by a plasma–surface phenomenon that probably involves recombination of nitrogen atoms.     

Duplex surface layer treatment of Al alloy: electron beam alloying and plasma nitriding

Abstract

Al alloys offer a high potential as lightweight construction materials due to their low density, specific strength and processing properties. However, the field of application is limited by their low hardness and poor wear properties. Duplex surface treatment combining electron beam (EB) alloying and plasma nitriding offers one possibility to produce hard and wear resistant surface layers on Al alloys. The EB alloyed surface layer acts as supporting layer for the hard AlN coating so that the load bearing capacity can be enhanced. In the present study duplex treatment of Al-5083 (AlMg4·5Mn0·7) Al alloy has been investigated. Before the EB treatment alloying material deposition was carried out by atmospherically plasma spraying. Various sandwich layers based on Al and Fe respectively, have been applied. Different beam deflection techniques have been tested and their effect on surface deformation, microstructure and hardness was evaluated. Plasma nitriding was carried out in order to evaluate the nitriding behaviour of the surfaces modified by EB. Applying the EB meander technique results in smooth surfaces, good microstructural connection to the matrix material and a homogeneous distribution of the alloying elements together with an increase in hardness of ～300 HV0·1. Plasma nitriding leads to the formation of AlN layers of ～5 μm thickness.     

离子渗氮技术及其应用

离子渗氮技术的理论基础是气体辉光放电特性,具有渗氮质量稳定,节能减排等优点。多种材料及不同条件下服役的零件经离子渗氮后,在表面硬度、渗层深度、硬度梯度、畸变量等方面均能达到相关的技术要求。介绍了一些典型工件进行离子渗氮的实例,并指出了生产中离子渗氮方面尚需解决的问题。     

On the problem of intensification of nitriding of titanium alloys

Ways of intensifying the process of nitriding titanium alloys in molecular nitrogen are considered. It is shown that by diminishing the partial pressure of nitrogen, changing the thermokinetic parameters of the saturation, using elements of vacuum technology, and allowing for the original structure and texture of titanium alloys, the process of their nitriding can be intensified with elimination of the negative aspects of high-temperature saturation. The obtained nitrided layers are analyzed from the standpoint of their functional properties. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 9–12, June, 1999.     

Distinctive features of diffusion layers formed by ion-beam nitriding of α and α + β titanium alloys at 500 to 1000°c

Besides unalloyed titanium, titanium alloys are coming into increasing use in technology today. The application of titanium alloys, however, has been limited by the low resistance to various types of wear as well as a tendency to adhere and become scratched during work in subassemblies involving friction. It is thus of interest to develop a method of surface hardening of these materials to improve their wear resistance. The article reports the results of studies on the structure of diffusion layers in a and + titanium alloys after ion-beam nitriding.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 34–37, May, 1994.