TC4钛合金表面激光合金化制备Ti-Si涂层

以Ti、Si单质元素混合粉末为原料,采用激光合金化技术在钛合金表面成功制备出了Ti-Si合金涂层。分析了涂层的组织形貌、成分和物相组成,测试了涂层的显微硬度及与YG6在干摩擦磨损条件下的摩擦磨损性能。结果表明:在合适的激光合金化参数下制备的Ti-Si涂层整体均匀致密,无裂纹且与TC4基体呈良好的冶金结合;涂层组织主要由针状的α-Ti基体和网状分布的Ti_5Si_3/β-Ti共晶体(室温下为Ti_5Si_3/α-Ti)组成;自下而上涂层组织细化,硬度HV在6600~7300 MPa之间,与TC4钛合金相比,平均摩擦系数降低(0.39 vs 0.45),耐磨性提高2.4倍。     

Surface alloying of iron-carbon alloys using laser heating

In recent years, laser radiation has been increasingly used for surface treatment of machine and tool parts. In cases when laser technologies can be cost-competitive, they have begun to displace traditional treatment methods. In this paper, we consider the structure of low- and medium-carbon structural steels after surface alloying using laser heating.Moscow State Highway Institute (Technical University). Translated from Metallovedenie i Termicheskaya Obrabotka. Metallov, No. 12, pp. 2–7, December, 1994.     

Ti6Al4V钛合金表面激光合金化制备Ti-Cu合金层的组织结构

采用激光合金化技术在Ti6Al4V合金基体表面制备了厚度约为120 μm均匀致密连续的Ti-Cu合金层,分析了合金层的元素分布和显微组织结构。结果表明,Ti-Cu合金层中Cu元素随着合金层深度呈梯度分布,在靠近Ti-Cu合金层表面的区域主要是柱状晶夹杂着少量的块状晶,中上部区域主要是生长取向各异且较粗的不发达枝状晶和部分胞状晶,中下部区域主要是生长取向各异的胞状晶,合金层与基材的界面处主要以细小的平面晶为主。合金化层中Cu元素和Ti元素除了形成固溶体外,还形成了Ti₂Cu、Ti₃Cu和Cu₃Al₄等金属间化合物,同时还形成了Cu₃TiO₄和Al₂TiO₅等金属陶瓷相。     

Microstructure and thermal stability of a Ni-Cr-Co-Ti-V-Al high-entropy alloy coating by laser surface alloying

A Ni-Cr-Co-Ti-V-Al high-entropy alloy (HEA) coating with a BCC phase and (Ni, Co)Ti₂ compounds was synthesized successfully by laser surface alloying on a Ti-6Al-4V substrate. The microstructure of as-synthesized coatings is typical, namely, the microstructure from the coating to the substrate changes from equiaxed grains to columnar grains. After remaining at 900 °C for 8 h, the constituent phases remain unchanged. However, owing to the unceasing dissolution of the Ti element, the lattice parameter of the BCC HEA phase changes from 3.06 Å to 3.16 Å. The thermoanalysis results show that the oxidation film on the Ni-Cr-Co-Ti-V-Al HEA coating is mainly composed of TiO₂, V₂O₅, and NiO. The oxidation resistance of this HEA coating may be due to the existence of NiO and the alloying elements Al, Cr, and Co; the oxidation phenomenon should be responsible for the mass increase in the thermogravimetry process. The differential scanning calorimetry and the dynamic differential scanning calorimetry curves show that the synthesized HEA coating is stable below 1005 °C.     

机械合金化法制备金锡合金

采用高能球磨机械合金化法制备了Au-20%Sn合金,分析了合金物相、组织和硬度随球磨时间的变化规律,探讨了合金塑性与合金组织及制备工艺的关系。结果表明:采用高能球磨机械合金化法可以制备Au-20%Sn合金;随球磨时间的增加,Au-20%Sn的合金化程度增加,组织中的金属间化合物逐渐增多,最终基本上为δ相和ζ′相;合金的硬度随球磨时间的延长逐渐升高,并在球磨60min后获得最高硬度104.2HV,然后开始下降;球磨后的合金粉末在190℃×2h的烧结过程中发生了不同程度的再结晶和晶粒长大,再结晶程度随球磨时间的延长而增加,导致烧结后合金硬度在球磨时间超过60min后反而下降。     

Surface hardening of steels by alloying with laser heating and subsequent chemical heat treatment

The necessity of providing a high set of operating properties has stimulated the development of combined technologies of surface hardening. A combination of laser alloying of low-carbon steels by nitride-forming elements (V, Cr, Mo, Al) with subsequent chemical heat treatment seems promising in this respect. Such a combined treatment provides a favorable distribution of residual stresses, elevates considerably the microhardness of the strengthened layers, and increases the wear resistance by a factor of 1.5–3 compared to nitrided nitralloys like steel 38Kh2MYuA. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 11–14, July, 1997.     

Surface alloying of AZ91E alloy by Al–Zn packed powder diffusion coating

A new surface coating technique, namely packed powder diffusion coating (PPDC), for AZ91E magnesium alloy is reported. This new technique uses a powder mixture of aluminium and zinc as diffusion source and produces uniform and thick coatings at temperatures below 420 °C. Experimental results showed that zinc in the powder mixture significantly promotes the formation of intermetallic layers on the surface of the magnesium alloy at process temperatures between 350 °C and 413 °C, which is more than 50 °C lower than the previously reported processes. Depending on the temperature and the Zn-content in the powder, X-ray diffraction analysis identified three intermetallic phases and Mg(Al, Zn) solid solution that consist of the surface alloyed layer. The intermetallic compounds are τ-Mg₃₂(Al,Zn)₄₉, φ-Al₅Mg₁₁Zn₄ and β-Mg₁₇(Al,Zn)₁₂. The hardness of the over 500 μm thick surface alloyed layers is up to four times higher than the substrate. Both the β-Mg₁₇(Al,Zn)₁₂ phase and the τ-Mg₃₂(Al,Zn)₄₉ phase show one to two order magnitude higher corrosion resistance than the α-phase (solid solution) and the φ-Al₅Mg₁₁Zn₄ phase in 5% NaCl solution. A process parameter window for the layer thickness as well as a schematic model for the formation of the layer is proposed. The PPDC process is a promising technique that provides effective protection of AZ91E alloy from both wear and corrosion.     

TC4钛合金表面激光NiAl-VC复合合金化的试验研究

为了改善钛合金表面性能,采用CO2激光器在钛合金表面进行了NiAl-VC复合合金化试验,分析了合金化层的组织结构和物相组成,测试了合金化层的显微硬度.结果表明,由于温度梯度和冷却速度的差异,合金化层的最表层、次表层与中下层呈现出不同的组织结构.合金化层与基体实现冶金结合,合金化层含有TiC、Al2NiTi3C、NiTi、Ti2 Ni及Ti3Al多种增强相,使得其显微硬度达996 HV0.1,比基体有较大提高.     

机械合金化法制备Al—Cu—Fe纳米非晶合金

采用行星式高能球磨机制备了Al80-xCuxFe20(x=20-40）三元非晶纳米合金粉末,分析了不同球磨时间及热处理工艺对粉末结构、颗粒大小等的影响。结果表明：成分为Al40Cu40Fe20的粉末球磨时逐步非晶化,球磨33h后,非晶化程度最大,最小颗粒尺寸达到5．6nm;进一步球磨,非晶晶化,颗粒尺寸增大;成分为Al80-xCuxFe20(x=20,25,30)的粉末球磨90h后,得到非晶,最小颗粒尺寸为3．4nm。球磨制备的Al-Cu-Fe非晶粉末具有铁磁性。用DSC测量了其晶化温度（Tc),Tc≈873℃。     

Formation of coatings of mixed aluminum and manganese oxides on the AL25 alloy

Features of plasma electrolytic oxidation of the AL25 cast complex-alloyed aluminum alloy are discussed. It has been shown that a variation in the nature and concentration ratio of the electrolyte compo- nents provides the formation of mixed-oxide coatings containing the materials of the basic matrix and the dopant. An increase in the coating thickness and the manganese oxide content in the coating is achieved by the homogenization of the treated surface owing to the simultaneous formation of oxides and the removal of alloying components of the alloy from the surface layers. Current density intervals that provide a uniform distribution of elements in the coating and a high efficiency of the Faraday and thermochemical reactions are determined. It is found that the stoichiometric oxygen index in MnO_x oxides is x = 1.71–1.87. Testing of the synthesized oxide systems in the model oxidation of carbon(II) oxide to CO₂ shows that the ignition and complete conversion temperatures are at the level of values characteristic of platinum catalysts.     

Surface alloying of an Mg alloy subjected to surface mechanical attrition treatment

A 100  200 μm thick Al-enriched surface alloyed layer was formed on an AZ91D Mg alloy subjected to surface mechanical attrition treatment and diffusion coating at temperature as low as 400 °C. Transmission electron microscopy observations indicated the formation of a large volume fraction of pearlite-like lamellar microstructure within the surface alloyed layer, which was identified to be Mg₁₇Al₁₂ precipitates (γ phase) in Mg solid solution matrix. The Al-enriched alloyed layer enhanced the wear resistance of the alloy in comparison with the un-treated AZ91D Mg alloy substrate under the same dry sliding wear condition. Examination of the worn surface indicated that the enhanced wear resistance of the alloyed layer was mainly attributed to the strengthening effect of γ phase.     

Fe---Cr---Ni---Mo---C alloys produced by laser surface alloying

Several Fe---Cr---Ni---Mo---C alloys were produced by laser alloying on plain carbon steel substrates, using the blown powder technique. It was found that a careful selection of the laser treatment parameters results in alloyed layers free of defects and with a homogeneous chemical composition. The structures were martensitic, fully austenitic and austenitic-ferritic, depending on the chemical composition. The high cooling rates were found to affect the austenitic-ferritic structures, which showed a larger quantity of δ ferrite than that predicted by the Shaeffler diagram. Surface alloys produced by laser processing, with chemical composition similar to that of conventional austenitic stainless steels, showed better pitting corrosion resistance than their bulk counterparts produced by conventional techniques, despite their higher carbon content.     

2A02航空铝合金激光冲击诱导的表层纳米化

采用输出波长为1064 nm、脉冲宽度为20 ns的调Q钕玻璃激光,对2A02航空铝合金板表层进行了激光冲击,用透射电镜及其高分辨像的傅里叶过滤像分析了激光冲击后样品表面的微结构演变,研究了激光冲击诱导的纳晶化行为与形成机理及其对表面性能的影响。结果表明,激光冲击能在2A02航空铝合金板表面形成直径为～100 nm的纳米晶;表面纳晶层的硬度比基体提高54.5%。分析认为2A02铝合金表面纳晶化过程是激光冲击超高应变率和超高能量共同作用下由位错和空位等非平衡缺陷诱导的晶粒分化过程。     

机械合金化合成Sn-Cu二元合金粉体

采用高能球磨的机械合金化法合成Sn-Cu二元合金超细粉体,对在球磨过程中粉体的结构演变、颗粒形貌、粒径分布及熔化特性进行了研究,讨论了合金化机制.结果表明:球磨粉体由Sn(Cu)过饱和固溶体及Cu6Sn5构成.在球磨初期,Cu、Sn颗粒相互迭加、冷焊,形成复合层块;随后,复合层块断裂碎化,球形颗粒相互团聚构成大的团粒;最后,团粒解散,小颗粒进一步细化.球磨60 h后,Sn-Cu合金粉体的平均粒径(d50)为1～3 μm,且随Cu含量由0.7 wt%增加到10 wt%,Sn-Cu合金粉颗粒形貌由不规则绒絮状变化到球状,熔点由231℃降低到288℃.     

TC4钛合金表面激光合金化涂层的组织与耐磨性能

采用WC(含碳量0.1wt%)、Ni、Si混合粉末为原料,利用激光合金化技术在TC4钛合金表面原位制备了含WC、Ni、Si的涂层,使用扫描电镜(SEM)、X射线衍射(XRD)与能谱分析(EDS)等方法分析了涂层的组织与成分,用HXD-1000B型维氏显微硬度计和MMW21型立式万能摩擦磨损试验机测试了涂层的显微硬度及摩擦磨损性能。结果表明:利用优化后的激光合金化参数制备出的含WC量较多的涂层,其整体均匀致密、无裂纹,且与TC4合金基材呈冶金结合;涂层物相主要由α-Ti、Ti₅Si₃、WC和TiNi组成;涂层硬度为950 HV0.2,平均摩擦因数为0.2,平均磨损量为0.308 mg,耐磨性显著提高。     

FeCoCrNiAlx高熵合金的电爆合金化

电爆喷涂是一种表面改性的新方法,它是利用高电压对喷涂材料脉冲放电,瞬时大电流将其加热并发生爆炸,产生高温粒子伴随冲击波喷射到基体表面形成涂层。本文提出了电爆法制备高熵合金涂层的新工艺,利用XRD、SEM、EDS以及电流电压波形对该方法制备高熵合金涂层的可行性进行了研究。结果表明,FeCoCrNiAlx (x=0, 0.5, 1.0)合金系涂层都形成了简单的FCC、BCC及FCC+BCC结构固溶体,并且随着Al含量的增加,该涂层的相结构由FCC相逐渐向BCC相转变。涂层表面平整、致密,没有明显的裂纹,且元素均匀分布在涂层表面,并没有发现明显的元素偏聚现象。初始充电电压11kV下的能量沉积为285.770 J,平均沉积效率达到48.8%。随Al含量的增加,涂层显微硬度逐渐增大,当x=1.0时平均显微硬度达到最大值531.8HV,大约是基体显微硬度的2倍。可以看出,电爆法实现了高熵合金涂层的成功制备。     

Oxidation resistance of TiAl alloy treated by plasma Nb-C alloying

In this paper, the duplex treatment of plasma surface niobizing and carburization (Nb-C alloyed or duplex treated) has been performed on TiAl substrates. Cyclic-oxidation tests for untreated and duplex treated TiAl were carried out in static air at 900 °C for 103 h. The mass gain due to oxidation was measured using an electrobalance. The chemical compositions of the Nb-C alloyed layer as well as its microstructure were examined by glow discharge spectrum (GDS) and the optical microscopy (OM). The electronic diffraction spectrum (EDS) and scanning electronic microscopy (SEM) were used to analyze and observe the oxide layers. The phase structures of the oxide scale were identified by X-ray diffraction (XRD). The results show that the oxidation rate of the duplex treated TiAl specimens decreased significantly, compared with the untreated TiAl. The roles of duplex treatment for improving the oxidation resistance are discussed.