搅拌摩擦加工制备Al3Ni-Al原位反应复合体

通过在搅拌摩擦加工(Friction Stir Processing,FSP)过程中填加微米级Ni粉的方法,利用Al、Ni在FSP条件下的快速原位反应,在Al合金1100-H14表面层获得Al3Ni-Al复合体。采用SEM、EDS以及XRD对表面复合体微观结构及相组成进行分析,并对其显微硬度进行评测。结果表明,在FSP强烈的热、力耦合作用下,Ni粉产生了充分碎化,破碎后的Ni粒子与Al产生快速原位反应,生成亚微米甚至纳米级Al3Ni颗粒,而少量微米级残留Ni颗粒被Al3Ni包裹,并与细小的Al3Ni颗粒一同均匀分布于Al合金基体中,从而使得表面复合体的硬度显著提高,其平均值达到了818.3MPa,为基体硬度的2.4倍。     

钛合金表面辉光离子渗铝耐蚀性

利用双层辉光离子渗金属技术,在钛合金(Ti6Al4V)表面渗AI,形成均匀的钛铝合金扩散层.用显微硬度仪测量渗层的显微硬度,用SEM、XRD分析渗层的截面形貌和相结构,并在0.5 mol/L H2SO4溶液和3.5%NaCl溶液中测试极化曲线方法.结果表明:经950℃,保温5 h后Ti6Al4V合金基材表面形成厚度约为20 ìm的钛铝合金扩散层,扩散层由金属间化合物Ti3Al和TiAl组成;合金表面显微硬度值达到8100 MPa;钛合金表面的耐蚀性能提高.     

搅拌摩擦加工制备镁合金表面复合层的显微组织和力学性能

选用轧态AZ31镁合金为基体、C60颗粒为增强相,采用搅拌摩擦加工技术(FSP)制备镁合金表面复合材料,搅拌针头旋转速度为600 r·min~(-1),加工速度为118 mm·min~(-1),分别进行1～3道次FSP加工后,通过金相、透射、硬度和拉伸等测试,对搅拌加工区复合显微组织和力学性能进行表征分析。研究表明:FSP可使镁合金晶粒显著细化; C60加入后,在1～3道次FSP内,随着加工道次升高,C60分散程度上升,复合材料平均晶粒尺寸降低,材料硬度上升,抗拉强度上升,但弥散于晶间的团聚颗粒使其拉伸性能低于母材;添加C60后的试样中,2道次硬度有明显上升,最高硬度可达母材的1. 73倍,3道次试样硬度平均值最高。结果表明,可通过FSP制备镁基表面复合层强化材料。     

铝合金搅拌摩擦加工制备颗粒增强表面层的组织演变机制

采用搅拌摩擦加工技术,对热喷涂高速钢涂层的铝合金进行了4次重复加工。测试分析结果表明,搅拌摩擦区域的显微组织经历了:涂层破裂→破碎成大尺寸颗粒并嵌入到基体中,并导致基体产生裂纹→大尺寸颗粒继续破碎,小尺寸的颗粒增加,部分块状颗粒被卷入到基体内部,裂纹因回复和再结晶而消失→细小颗粒均匀分布的表面复合层一系列演变过程。由于强烈的热、力耦合作用,使Al-Fe间产生了异常的快速互扩散,搅拌摩擦加工过程中生成的大量细小的Al3Fe颗粒。表面复合层显微硬度最高达到540 HV,比基体的提高了近8倍。     

溶渗法制备Al3Ti/Al复合材料的研究

以钛丝网为反应源,以金属Al为基体,通过熔渗+原位反应法制备出一种Al3Ti金属间化合物颗粒增强铝基表面复合涂层。根据差热分析结果确定了反应温度为890℃;通过XRD、SEM以及显微硬度和磨损测试对所得到的复合涂层进行了表征。结果表明:当保温时间为20 min时,钛丝在铝基体中的反应较完全,原位合成为块状和条状的Al3Ti颗粒;颗粒的显微硬度大约为基体的4.5倍;在载荷为10 N的干滑动磨损条件下,相对于没有增强的Al基体而言,保温20 min所制备的复合涂层表现出较好的耐磨性,其磨损机制为粘着磨损和磨粒磨损共存。     

原位合成Al_3Ti颗粒增强铝基复合涂层(英文)

以直径200μm、纯度99.5%的钛丝丝网为反应源,通过熔渗-原位反应法制备一种Al3Ti金属间化合物颗粒增强铝基表面复合涂层。差热分析结果表明,在890°C下,Ti丝和Al熔体间发生反应。采用XRD、SEM以及显微硬度和磨损测试对所得到的复合涂层进行表征。结果表明:当保温时间为20min时,钛丝反应完全,原位合成为块状和条状的Al3Ti颗粒;颗粒的显微硬度大约为基体显微硬度的4.5倍;在载荷10N的干滑动磨损条件下,与没有增强的Al基体相比较,保温20min所制备的复合涂层表现出较好的耐磨性,其磨损机制为粘着磨损和磨粒磨损共存。     

搅拌摩擦加工制备具有单一和混合表面的Al5083/CeO_2/SiC复合材料的显微组织和磨损行为（英文）

利用搅拌摩擦加工(FSP),将纳米尺寸的氧化铈(CeO_2)和碳化硅(SiC)颗粒以单独和混合形式嵌入Al5083合金基体,制备表面复合材料,并研究这些增强相对合成的表面复合层显微组织和耐磨性能的作用。在室温下用销-盘式磨损试验机检测合成的单独和混合表面复合层的磨损特性。用光学显微镜和扫描电镜观察FSPed区和磨损表面的显微组织。在熔核区可观察到显著的晶粒细化和均匀分布的增强颗粒。与基体金属相比,所有复合材料都具有更高的硬度和更好的耐磨性。其中,混合复合材料Al5083/CeO_2/SiC的耐磨性能最好,摩擦因数最低,而Al5083/SiC的硬度最高,是Al5083基体合金硬度的1.5倍。混合复合材料表面耐磨性能的提高是由于CeO_2颗粒的固体润滑效果。非复合材料中主要的磨损机制是严重的粘着磨损,当存在增强颗粒时转变为磨粒磨损和分层。     

真空热处理对Ti6Al4V基体/NiCrAlY涂层体系组织结构及元素扩散行为的影响

采用电弧离子镀(AIP)技术在Ti6Al4V基体表面沉积制备了NiCrAlY涂层. 通过金相观察(OM)、扫描电镜(SEM)与能谱(EDS)分析、 X射线衍射(XRD)分析以及显微硬度测试, 研究了真空热处理对NiCrAlY涂层组织性能的影响, 讨论了Ti6Al4V基体/NiCrAlY涂层界面元素扩散规律. 结果表明: 700.℃真空热处理后, NiCrAlY涂层中开始析出γ′-Ni3Al相, 这提高了涂层的表面硬度; 在700.℃温度下, Ti6Al4V基体/NiCrAlY涂层界面由外至内出现Ni3(Al,Ti)、 TiNi和Ti2Ni中间化合物层, 并随着温度提高, 界面处中间化合物层增厚; 700.℃时, 主要发生了镍、钛元素的扩散, 铬元素在870.℃开始发生扩散. 当温度提高到950.℃后, 由于镍元素大量向Ti6Al4V基体扩散引起涂层的退化失效.     

搅拌摩擦加工技术制备Ti颗粒增强AZ31镁基复合材料

利用搅拌摩擦加工技术制备Ti颗粒含量为20%(体积分数,下同)与40%的Mg-AZ31基复合材料.结果表明:碎化后的Ti颗粒平均尺寸约为200 nm,经4次搅拌摩擦加工处理后基体组纵发生明显的细化,晶粒尺寸为3～5 μm.添加20%Ti颗粒的复合层中碎化的Ti颗粒在Mg基体中呈不均匀分布,复合层具有较低的强度和伸长率;当Ti颗粒添加量为40%时,复合层中碎化Ti颗粒在Mg基体中均匀分布,复合层强度有明显提高,伸长率较基体无明显降低.利用混合定律计算复合层的显微硬度,其结果与试验值相吻合.     

5083铝合金表面镀钛/渗氮复合层组织结构与摩擦学性能北大核心CSCD

通过镀/渗复合改性方法在5083铝合金表面原位制备出梯度复合层,利用闭合场非平衡磁控溅射离子镀在5083铝合金表面沉积厚度约为6.0μm的Ti膜,然后将镀钛5083铝合金在490℃进行等离子渗氮8 h,研究了不同渗氮气氛(微量N,N-H比为0.05∶0.3,0.2∶0.3和0.3∶0.3)对复合层组织结构和力学性能的影响。结果表明:复合层由双层结构组成,即外层TiN_(0.3)和靠近铝基体一侧的铝基金属化合物Al_(18)Ti_2Mg_3,不同渗氮气氛下表层TiN_(0.3)均出现(002)晶面择优生长,在N-H比为0.2∶0.3时,复合层的表面硬度高达880 HV,相比于未处理的基体铝合金硬度(98 HV)提高了约9倍。复合层的摩擦系数明显低于未处理态,并且磨损率显著降低。     

In situ formation of various intermetallic particles in Al–Ti–X(Cu,Mg) systems during friction stir processing

In situ Al composites reinforced by various intermetallic particles were fabricated from Al–Ti–X(Cu, Mg) systems by hot pressing, forging and subsequent 4-pass friction stir processing (FSP). The formation of various intermetallic particles during FSP and the tensile properties of in situ composites were investigated. For Al–Ti–Cu system, Cu enhanced the Al–Ti reaction and resulted in the formation of more Al₃Ti particles due to the presence of a small amount of liquid phase during FSP. After FSP, part of Cu was kept in the Al matrix as solute, whereas the other formed Al₂Cu particles. For Al–Ti–Mg system, except for Al₃Ti, some Ti₂Mg₃Al₁₈ particles with fine twin lamellas were formed during FSP, resulting in an increase in the total volume fraction of reinforcing particles. Cu and Mg addition increased the strength of the in situ composites substantially due to introduction of more strengthening modes and more reinforcing particles, however the elongation decreased dramatically.     

Formation of surface layer based on Al3Ti on aluminum by laser cladding and its compatibility with ceramics

Intermetallic compound Al₃Ti or intermetallic compound matrix composite (IMC) surface layers were formed on Al surface by laser cladding. To form sound IMC surface layers, laser conditions must be controlled to suppress the melting of base metal. With increasing the volume fraction of ceramics in the IMC layer, it needed higher laser power to obtain IMC layer although the control of laser conditions became easier. During laser cladding, TiB₂ melted by laser irradiation and then homogeneously precipitated as fine particles at a cooling stage. On the contrary, TiC and SiC hardly melted and were dispersed in Al₃Ti matrix. SiC reacted with Ti to form titanium-silicide or TiC, which made the composition of matrix richer in Al than Al₃Ti and caused degradation of the wear property. IMC surface layer improved the wear property of Al substrate. The particle size as well as volume fraction of dispersoid ceramics affected the wear property.     

Reactive mechanism and mechanical properties of in situ composites fabricated from an Al–TiO2 system by friction stir processing

In situ (Al₃Ti + Al₂O₃)/Al composites were fabricated from powder mixtures of Al and TiO₂ using hot pressing, forging and subsequent multiple-pass friction stir processing (FSP). The reactive mechanism and mechanical properties of the FSPed composites were investigated. Four-pass FSP with 100% overlapping induced the Al–TiO₂ reaction, as a result of the enhanced solid diffusion and mechanical activation effect caused by the severe deformation of FSP. Decreasing the size of TiO₂ from 450 to 150 nm resulted in the formation of more Al₃Ti and Al₂O₃ particles. The formation mechanisms of Al₂O₃ and Al₃Ti during FSP are understood to be a deformation-assisted interfacial reaction and deformation-assisted solution-precipitation, respectively, based on detailed microstructural observations. The microhardness, Young’s modulus and tensile strength of the FSPed composites were substantially enhanced compared with those of FSPed pure Al with the same processing history, and increased as the TiO₂ size decreased from 450 to 150 nm. The strengthening mechanisms of the FSPed composites included load transferring, grain refinement and Orowan strengthening, among which Orowan strengthening contributed the most to the yield strength of the composites.     

Formation of Al–Mo intermetallic particle-strengthened aluminum alloys by friction stir processing

This study investigated the formation of Al–Mo intermetallic particle-strengthened aluminum alloys from the mixture of Al and Mo powders by using friction stir processing (FSP). The FSP resulted in considerable plastic deformation and heat input from the rotating pin and its shoulder against the sample. In this process, the hot working nature of FSP can effectively promote the exothermic reaction between Al and Mo to produce fine Al–Mo intermetallic particles with an average size of approximately 200 nm. The Al–Mo intermetallic particles formed during FSP were identified mainly as Al₁₂Mo with a small amount of Al₅Mo. The Al–Mo reaction during heat treatment without the help of concurrent shear deformation was relatively slow because it was controlled by the interdiffusion through the Al₁₂Mo phase. The critical mechanism responsible for the rapid reaction and the formation of nanometer particles in FSP was the effective removal of the Al₁₂Mo phase from the Al–Mo interface, which was caused by the shear force imposed by the rotating tool pin.     

Synthesis of titanium aluminide coatings on aluminum and titanium surfaces by mechanical alloying and subsequent annealing

Intermetallic Ti-Al-based coatings were synthesized by mechanical alloying in a vibratory ball mill and subsequent annealing. A titanium layer was deposited on aluminum specimens and an aluminum layer and aluminum-titanium mixture were deposited on titanium specimens. Under the effect of milling balls, powder particles deposit at the substrates, forming layers that have a very good cohesion with the substrate. During subsequent heating, diffusion layers on the basis of titanium-aluminum phases are synthesized as a result of the chemical interaction between titanium and aluminum. In the case of titanium layer deposited on aluminum, the temperature interval of transformations is 600–650°C; first, a Ti₃Al₅-based phase is formed; then, as diffusion saturation with Al increases, an Al₂Ti-based layer appears; and finally, the Al₃Ti compound is formed. The reaction rates depend on the temperature and the duration of annealing. On titanium with a (Ti + Al) layer deposited on its surface, the Al₃Ti, Al₂Ti, TiAl, and Ti₃Al compounds are formed in a temperature interval of 600–900°C. In the case of deposition a homogeneous aluminum layer on titanium, only Al₃Ti and Ti₃Al phases were observed after annealing.     

Microstructures and wear resistances of hybrid Al–(Al3Ti+Al3Ni) FGMs fabricated by a centrifugal method

The Al based functionally graded materials (FGMs), reinforced by a hybrid of Al₃Ti platelets and Al₃Ni granular particles, were fabricated by the centrifugal method with both ingots of commercial Al–5mass%Ti and Al–20mass%Ni master alloys. The ratios of Al–Ti and Al–Ni alloys were 3:1, 1:1 and 1:3 (in mass), and the applied G numbers are 30, 50 and 80. The microstructures of hybrid Al–(Al₃Ti+Al₃Ni) FGMs were observed with an optical microscope (OM) and a scanning electron microscope (SEM). Since the gradient distributions in orientation of Al₃Ti platelets and in particle size of Al₃Ni primary crystal particle were expected to be formed in the fabricated hybrid Al–(Al₃Ti+Al₃Ni) FGMs, detail observations of the orientation of Al₃Ti platelets and the size of Al₃Ni granular particles were performed. The wear resistance of the FGMs was measured by an Okoshi-type wear machine. Based on the experimental results, the advantages of hybrid Al–(Al₃Ti+Al₃Ni) FGMs were discussed.     

Fabrication of Al/Al2Cu in situ nanocomposite via friction stir processing

The aim of present work is fabrication of Al/Al₂Cu in situ nanocomposite by friction stir processing (FSP) as well as investigation of FPS parameters such as rotational speed, travel speed, number of FSP passes, and pin profile on the microstructure, chemical reaction, and microhardness of Al based nanocomposite. The Al₂Cu particles were formed rapidly due to mechanically activated effect of FSP as well as high heat generation due to Al-Cu exothermic reaction. The microstructure of the nanocomposites consisted of a finer grained aluminium matrix (～15 µm), unreacted Cu nanoparticles (～40 nm), and reinforcement nanoparticles of Al₂Cu. Irregular morphology of Al₂Cu is attributed to the local melting during FSP. Pin diameter has a higher effect on the microstructure and hardness values. The hardness measurements exhibited enhancement by 57% compared with the base metal.     

Crystallography and refining mechanism of （Ti,B）-contained salts in pure aluminum

It is shown from experiment that the pure B contained salt exhibits little refining effect, while the pure Ti contained salt, especially the salt containing 5Ti/1B, shows obvious refining effect on the pure aluminum. Crystallographic study indicates that AI3Ti particle is a more suitable nucleation site for the aluminum matrix than （Ti, A1）B2 type particles （TiB2, A1B2 and （Ti,A1）B2）, because there exist more coherent planes with aluminum matrix in the former. Thermodynamics estimation, X-ray diffraction （XRD） and SEM detection show that the refining mechanism of （Ti, B）-contained refiners is mainly contributed to the heterogeneous nuclei of fine Al3Ti particles dispersed in the melting, which comes from the reaction between the Ti and aluminum. （Al, Ti）B2 type particle shows little or no direct refining effect, but it will reduce the size of Al3Ti since the Al3Ti nucleates and grows along the （A1, Ti）B2 type particle interface.     

Effect of si addition on mechanical alloying behavior and creep properties of Al-10Ti-xSi alloys

Al-10Ti-xSi alloys (x=0∼6wt.%) have been mechanically alloyed under Ar atmosphere using an attritor and the alloying process has been investigated. From Al-10Ti composite powders, supersaturated Al(Ti) powders were obtained after mechanical alloying. In the ternary mixture, fine Si particles were observed to be distributed in the Al(Ti) matrix due to both the negligible solid solubility of Si in the Al matrix and the weaker chemical interaction of Si with Al, as compared with Ti. The sealed compacts were hot extruded to full density at 450°C with an extrusion ratio of 12:1. The microstructures and creep properties of the hot extruded alloys were examined. During consolidation, Si particles were dissolved in Al₃Ti up to 4 wt.% Si to form the (Al(Si))₃Ti phase, and the Ti₇Al₅Si₁₂ phase was formed beyond the solubility limit of Si in Al₃Ti. The transition from the Coble creep mechanism at low stresses and temperatures to dislocation one at high stresses and temperatures was observed. The stress and temperature of the transition from diffusional to dislocation creep became higher as Si concentration increased. This was due to an enhancement of Al₃Ti particle strength with increasing Si content as a result of Si incorporation. Thus, the addition of Si enhances the creep resistance of the MA Al-10Ti alloy.     

Formation of a wear-induced layer with nanocrystalline structure in Al–Al3Ti functionally graded material

A new severe plastic deformation (SPD) process to obtain nanocrystalline (NC) structure by wear is reported. An Al–Al₃Ti functionally graded material fabricated by a centrifugal method is wear tested to investigate the microstructure of the wear-induced layer. When the sliding distance of the wear exceeds l = 100 m, the wear-induced layer is obtained just below the worn surface. The microstructure of the wear-induced layer consists of fine Al₃Ti fibrous particles and an NC solid-solution matrix containing a partly amorphized phase. The NC matrix has fine grains with a mean diameter of 16 nm and is a supersaturated solid-solution in which Ti is dissolved in the Al matrix. From the microstructure, it is estimated that the wear-induced layer is formed at a nominal shear strain of more than 90 and an effective shear strain of more than 52. An NC structured wear-induced layer is generated by the SPD process.