GH4169合金气体渗氮工艺研究

利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、能谱仪(EDS)、显微硬度仪等分析手段,对GH4169合金的渗氮机理及长时间气体渗氮后渗氮层和基体组织、成分、性能进行了分析.结果表明,GH4169合金渗氮层深度和渗氮时间符合抛物线规律,长时间气体渗氮后渗层中会析出均匀细小的CrN(尺寸在纳米级)、Cr7C3相.渗氮层硬度达到1 268 HV0.05,渗氮层较脆,裂纹易沿原始γ相晶界萌生并扩展.     

Principles of alloying of nickel alloys,hardenable by internal nitriding

Internal nitriding is a process of surface saturation with nitrogen, in which there forms a diffusion layer, consisting of nitride particles that are uniformly distributed in a solid solution but without a surface zone of continuous nitrides, as in conventional nitriding. This is achieved by selection of the alloy chemical composition and the nitriding process regimes. The presence of this diffusion layer opens up broad possibilities for the hardening of various alloys, since a high level of brittleness of the layer is avoided. This is an advantage over conventional nitriding.Moscow Highway Institute (MADI). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 5–8, March, 1994.     

激光辅助氮化工艺中的开裂行为研究

目的研究激光辅助氮化过程中,氮化层的开裂行为。方法利用CO2激光辅助氮化的方法在钛合金表面制备氮化钛涂层,观察氮化层的宏观、微观形貌,分析组织结构特征,测定氮化层残余应力,研究基体厚度、激光扫描工艺参数对氮化层表面形貌和裂纹情况的影响。结果钛合金经单道或多道激光氮化后,表面形成非均匀氮化钛层,其显微结构为沿主干轴交叉生长的枝状晶组织,存在数量和尺寸不等的显微裂纹。较薄试样经单道激光氮化后,表面呈现较低的残余压应力状态,较厚试样则以拉应力为主;试样经多道激光氮化后,整个氮化区表面均呈现残余压应力状态。结论枝状氮化层与基体组织高度结合,不易脱落,但受基体约束作用,氮化层内的拉伸热应力导致其冷却过程中形成微裂纹。随着试样厚度和氮化面积的增加,较高的热应力使得裂纹密度和裂纹尺寸增加,严重影响氮化层的质量。残余应力是热应力和相变应力叠加的结果,对于多道激光氮化工艺而言,大面积氮化使得相变压应力增加,同时后热效应使得热应力降低,最终呈现出残余压应力状态。     

Effect of nitriding on the electrochemical behaviour of Ti‐Al‐Mn alloy

The effect of technological conditions of nitriding such as process time duration and chemical composition of saturating medium, on the corrosion behaviour of nitrided coatings in 14 M solution of sulphuric acid was analyzed. The investigations were done on the alloy Ti‐5,0 Al‐2,0 Mn. The nitriding was carried out in nitrogen both at atmospheric pressure and rarefied nitrogen pressure (1 Pa) at the temperature 850°C and time processing in the range from 5 to 20 h in nitrogen‐containing gas only, and in powder electrode graphite and nitrogen‐containing gas. It was shown that technological conditions of nitriding determine the protective properties of nitrided coatings. It was indicated that the optimal structure of the nitride layer for best corrosion protection is the thin nitride TiN_x with high surface quality and a gas‐saturated layer. Nitriding in graphite powder effects positively the protective properties of nitride coatings due to reducing the nitride‐forming process.     

Nitride formation in titanium based substrates during laser surface melting in nitrogen–argon atmospheres

Laser nitriding of a commercial purity (CP) Ti and a near gamma TiAl based alloy in Ar–N₂ gas mixtures has been investigated both experimentally and theoretically. Observations indicate that the nitride TiN forms in CP Ti, while TiN and Ti₂AlN form in the near gamma alloy. Melt dimensions and temperature distributions, that correlate well with the phases observed, have been theoretically simulated using a three-dimensional analytical model of the heat transfer problem. A marked increase in melt volume is observed when the nitride phases are formed, and this has been attributed to the increase in the rate of laser power absorption induced by nitride formation rather than the exothermic heats of formation. Thermocapillary driven fluid flows, which increased with increases in the N₂ concentration of nitriding atmosphere and the laser–material interaction time play a major role in determining the shape and surface contours of the melt pool.     

High-temperature oxidation of nickel alloy with nitride strengthening

Isothermal oxidation of nickel alloy containing (wt %) Ni (main), Cr 25.1, Co 26.3, W 10.3, Ti 1.9, and Mo 1.2 was studied at temperatures of 1100 and 1200°C in air. The disperse particles of titanium nitride found to increase alloy heat-resistance. The aluminosiliconization of alloy strengthened by nitride particles at a depth of 45–50 μm decreases the oxidation rate of alloy strengthened by disperse particles of titanium nitride at temperatures of 1100 and 1200°C.     

Improvement in the high-temperature strength of alloys based on cobalt by internal nitriding

Internal nitriding, as for internal oxidation, may be considered as a particular case of material dispersion strengthening. Internal nitriding is accompanied by preparation of a heterophase structure of a diffusion layer: The matrix is a solid solution with fine particles of alloying element nitride particles distributed within it. Internal nitriding may be special importance as a version of dispersion hardening for high-temperature alloys. Possibilities are considered in this article for internal nitriding of cobalt alloys.Moscow Highway Institute (Technical University). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 7–11, December, 1994.     

High-temperature oxidation of nickel alloy with nitride strengthening

Isothermal oxidation of nickel alloy containing (wt %) Ni (main), Cr 25.1, Co 26.3, W 10.3, Ti 1.9, and Mo 1.2 has been studied at 1100 and 1200°C in air. It has been found that disperse particles of titanium nitride increase the alloy heat-resistance. Alumosiliconizing of the alloy strengthened by nitride particles to a depth of 45–50 μm decreases by an order of magnitude the oxidation rate of alloy strengthened by disperse particles of titanium nitride at 1100 and 1200°C.     

Corrosion resistance of Ti–6Al–4V alloy with nitride coatings in Ringer’s solution

The corrosion behaviour of Ti–6Al–4V alloy with nitride coatings was investigated in Ringer’s solution at 36 and 40 °С. Nitride coatings of different composition, thickness and surface quality were formed because of changing nitrogen partial pressure from 1 to 10⁵ Ра and nitriding temperature from 850 to 900 °С. Results shown that nitride coatings improve anticorrosion properties of alloy at both solution temperatures. Corrosion resistance of alloy increases with the content increase of TiN phase in nitride coating. With increase of temperature from 36 to 40 °С the corrosion resistance of alloy is determined significantly by quality of nitride coating.     

Corrosion resistance of the Ti-6Al-4V titanium alloy with nitride coatings in 0.9 % NaCl

The influence of temperature and pressure of nitriding on the corrosion resistance of Ti-6Al-4V titanium alloy in 0.9% NaCl was studied. It is shown that forming of nitride film improves the anticorrosion characteristics of the alloy regardless of the temperature of the corrosion environment. At the temperature of 36°C the pressure and temperature of nitriding positively influence the anticorrosion characteristics of the alloy. At 40°C the pressure positively influences the protection of the alloy surface, and the influence of the temperature factor is negative.     

High-Temperature Nitriding of Refractory Alloys

Processes of high-temperature internal nitriding of refractory alloys based on nickel and cobalt are described. Thermodynamic backgrounds for formation of zones of internal nitriding with optimum phase compositions in alloys containing alloying elements with different affinity for nitrogen are considered. It is shown experimentally that the structures obtained in zones of internal nitriding with segregations of stable fine nitride phases depend on the ratio of concentrations of the nitride-forming elements, on the nitriding temperature, and on the composition of the saturating atmosphere. The kinetic parameters of the process of internal nitriding and the conditions of formation of through diffusion layers are determined. It is shown experimentally that the refractory characteristics of the nitrided layers are enhanced.     

盐浴渗氮处理对FeCrMnNiAl0.2Ti0.1高熵合金组织及性能的影响

采用盐浴渗氮的化学热处理方法对FeCrMnNiAl_0.2Ti_0.1高熵合金进行表面强化,主要工艺为预热+盐浴渗氮+氧化,研究渗氮温度对渗层和性能的影响。采用光学显微镜、扫描电镜、X射线衍射仪研究不同渗氮温度下高熵合金的组织结构和物相,利用显微硬度计和W-2000摩擦磨损试验机分别测量硬度和耐磨性。结果表明,经过盐浴渗氮后,高熵合金表面形成含氮化物和氧化物的复合渗层,渗氮层深度最高为27.1 μm,硬度最高可达1080.0 HV0.2。盐浴渗氮可以有效提高高熵合金的耐磨性,改善摩擦学行为,640 ℃渗氮试样的磨损率仅为0.025 mm³/(N·m),与铸态相比降低了约76.7%。     

Vergleichende Untersuchungen über die Aufstickung von niedrig- und hochlegierten Stählen sowie der Legierung NiMo 16 CrW in Ammoniak bei 300 bis 500°C

Comparative investigations into the nitruration between low and high alloy steels and the alloy NiMo 16 CrW in ammonia at 300 to 5OO°C The nitriding behaviour of high temperature high strength steels 13 CrMo 44, 10 CrMo 910 and 17 CrMoV 10, of the high alloy high temperature strength steels X 8 CrNiNb 16 13, the stainless steel Y 8 Cr 17 and nickel base alloy NiMo 16 CrW has been studied in ammonia at 300, 400 and 5OO°C, test durations being up to 1000 hours. The evaluation was based on determination of the nitriding depth preferentially with the aid of microhardness measurements. The structure of nitride layers and the structure changes due to nitrogen adsorption in the material are explained in connection with the time dependence of nitriding. The behaviour of specimens Passivated in air is shown as well as the influence of the surface pretreatment by depassivation or preoxidation and the influence of minor oxidising constituents (air, steam) in ammonia.     

钛合金表面半导体激光气体氮化涂层的性能研究

目的提升钛合金(TC4)叶片表面性能,解决失效问题。方法实验采用激光局部气体氮化工艺代替传统氮化工艺,利用2 k W柔性光纤耦合半导体激光器在钛合金(TC4)基体表面采用气体氮化的方法制备TiN表面改性层。采用摩擦磨损试验机和改制的汽蚀装置分别测试了氮化层与基体(TC4)的耐磨性与抗汽蚀性能。结果摩擦磨损实验后,激光氮化层的质量损失为2.3 mg,基体TC4的质量损失为20.2 mg,激光氮化层的损失质量为基体TC4的11.3%,激光氮化层抗磨损性能相较基体TC4提高了7倍。TC4基体汽蚀损失的质量为4.08 mg,而氮化层的质量损失为1.13 mg,氮化层的抗汽蚀性能比基体提高了2.61倍。结论采用半导体激光气体氮化钛合金叶片能够得到分布着大量TiN枝晶的氮化层,提高表面耐磨损性能,氮化层中的TiN枝晶构成的网篮状组织对其表面抗汽蚀性能也有所提高。     

Effect of severe plastic deformation on the structure,microhardness, and wear resistance of the surface layer of titanium subjected to gas nitriding

The effect of severe plastic deformation under dry sliding friction on the structure, microhardness, and wear rate of the VT1-0 titanium subjected to gas nitriding has been studied. It has been shown that this deformation leads to the formation of a nanocrystalline structure with an α-crystal size of 10–100 nm and a microhardness of ～3.1 GPa in a surface layer up to 10 μm thick. The presence of this structure intensifies the saturation of the surface of the titanium with nitrogen in the course of subsequent gas nitriding at temperatures of 650–750°C. The formation of the nitride nanocrystalline TiN phase in the deformed titanium occurs at a relatively low nitriding temperature (700°C) and a short-term holding (2 h). The volume fraction of the nitride phase, which is formed in the layer up to 10 μm thick, reaches a few tens of percent, which leads to an increase in the microhardness of the nitrided surface of the titanium deformed by friction. Preliminary severe plastic deformation has a negative effect on the fatigue wear resistance of the nitrided titanium due to an increased brittleness of the deformed and subsequently nitrided surface layer of this material.     

冷轧预处理对TC4合金540 ℃渗氮组织的影响

TC4钛合金经820 ℃固溶处理及室温下冷轧得到10%、20%、30%、40%、50%不同变形量的试样,之后在540 ℃进行渗氮复合时效处理8 h。利用光学显微镜、X射线衍射仪、扫描电镜等分析了不同变形量下合金渗氮组织和时效组织的变化特点以及渗氮试样表面的相结构和形貌的变化。试验结果显示,渗氮处理后,试样表面生成了TiN、Ti₂N等高硬的氮化物颗粒,变形量越大,试样表面生成的氮化物颗粒越多且尺寸越大;经固溶处理后,TC4合金的室温组织为α相+亚稳β相,经渗氮复合时效处理后,亚稳β相分解为α相,同时α相向β相转化,变形量越大,析出的β相越多,且这种趋势不如单纯的时效处理明显。     

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。     

Corrosion behaviour of glow discharge nitrided titanium alloys

The aim of this work is the study of the corrosive behaviour of glow discharge nitrided Ti-6Al-4V alloy, using electrochemical techniques.Potentiodynamic polarisation and electrochemical impedance measurement show the excellent corrosive resistance of titanium alloy after thermochemical treatment, as well as different behaviour between the alloy before and after the nitriding treatment.Also, in very hostile environments, such as 5 wt.% HCl, where the titanium alloy is heavily corroded, the nitrided samples show good resistance. Nevertheless, 750 °C nitrided samples have worse behaviour than those treated at 900 °C. This is probably due to the lower corrosion resistance of the nitride ε present in the nitrided layer created at the lower temperature than the nitride δ, and the limited thickness of the modified layer obtained at this temperature.     

A study into effects of CO2 laser melting of nitrided Ti-6Al-4V alloy

Multiple treatment of engineering surfaces can provide improved surface properties that cannot be obtained by a single surface treatment. Consequently, this study investigates the effects of laser melting on the microstructures of plasma nitrided Ti-6Al-4V alloy. The study consists of two parts. In the first part, governing equations pertinent to the laser melting process are developed, and temperature variation across the melted zone is predicted. In the second, an experiment is conducted to nitride the surface of the alloy through plasma nitriding process and to melt the plasma nitrided and the untreated alloy surfaces with a CO₂ laser beam. The resulting metallurgical changes are examined using x-ray diffraction (XRD), bdenergy-dispersive spectrometry (EDS), and scanning electron microscopy (SEM) techniques. It is shown that three distinct nitride layers are formed in the vicinity of the alloy surface prior to the laser melting process, and that after the melting process nitrided species are depleted while cellular and dendritic structures are formed. In addition, the structure consisting of transformed β containing coarse and fine acicular α is observed in the melted regions.