α_2＋B2相区等温锻造及热处理对Ti-22Al-25Nb合金组织和性能的影响

研究了Ti-22Al-25Nb合金在α2＋B2相区等温锻造及不同制度热处理,其显微组织演变规律和室温、高温拉伸性能变化。结果表明：在α2＋B2相区等温锻造后显微组织仍由等轴α2相颗粒、O相包裹着的等轴α2相、细小板条状O相与B2基体组成,与原始锻棒组织的区别在于等轴α2相颗粒发生溶解,数量减少,尺寸下降;等温锻造后再在O＋B2相区固溶处理的,组织中等轴α2相颗粒分解,由等轴α2/O相颗粒、板条O相和B2基体组成,且随固溶温度升高,板条O相溶解,变粗、变短;等温锻造后经固溶加时效处理时,B2基体中析出二次针状O相,且随时效温度升高,二次针状O相变粗、变短,室温及650℃高温拉伸性能也随时效温度升高,表现为强度降低而塑性提高。     

热处理对近β锻造的多元Ti2AlNb基合金组织和性能的影响

以近β锻造的多元Ti2AlNb基合金Ti-22Al-25Nb-1Mo-1V-1Zr-0.2Si（at %）为实验对象,采用扫描电子显微镜（SEM）、透射电子显微镜（TEM）和万能拉伸试验机等测试手段研究了不同热处理对近β锻造Ti2AlNb基合金组织和力学性能的影响。结果表明：经近β锻造空冷后的组织由初生α2相、针状O相和基体B2相构成。随着固溶温度的升高,合金室温、高温强度升高,塑性降低。而随着时效温度的升高,合金的强度和塑性变化规律与固溶处理的规律正好相反。分析认为,固溶处理主要影响合金中初生α2/O相体积分数,随着固溶温度的升高,初生α2/O相体积分数减少,使得针状O相的强化作用增强,同时造成α2相对B2晶界钉扎减弱,B2晶粒长大塑性降低。时效处理主要影响析出相形态,随着时效温度的降低,合金中析出板条厚度减小,使得细小板条强化作用增加,而有利于塑性的B2相体积分数减少,导致合金塑性降低。     

Ti-22Al-25Nb合金等轴组织演变和拉伸性能

研究了Ti-22Al-25Nb合金等轴组织的演变及其对拉伸性能的影响。结果发现,经α_2+O+B2三相区等温锻后,在O+B2两相区固溶过程中,组织中初始O相板条粗化变短,冷却析出的细板条则溶解到B2基体中,α_2/O相颗粒不发生明显变化,固溶温度升高使得少量等轴O相发生溶解,rim O相厚度减小。而在O+B2两相区时效的过程中,大量细密的二次O相板条从B2基体析出,少量被rim O包围的α_2相向O相转变。时效温度升高时,析出的二次板条O相变得粗大,总体含量减少,rim O厚度增加。时效温度的升高还使得合金强度下降而塑性增加。     

Ti-22Al-25Nb合金等轴组织演变和拉伸性能研究

研究了Ti-22Al-25Nb合金等轴组织的演变及其对拉伸性能的影响。结果发现,经α₂+O+B2三相区等温锻后,在O+B2两相区固溶过程中,组织中初始O相板条粗化变短,冷却析出的细板条则溶解到B2基体中,α₂/O相颗粒不发生明显变化,固溶温度升高使得少量等轴O相发生溶解,rim O相厚度减小。而在O+B2两相区时效的过程中,大量细密的二次O相板条从B2基体析出,少量被rim O包围的α₂相向O相转变。时效温度升高时,析出的二次板条O相变得粗大,总体含量减少,rim O厚度增加。时效温度的升高还使得合金强度下降而塑性增加。     

固溶温度对Ti-22Al-24Nb合金显微组织的影响

研究了经开坯锻造的Ti-22Al-24Nb合金在不同固溶温度下的显微组织变化规律。结果显示:开坯锻造后Ti-22Al-24Nb合金的显微组织为等轴三相(α_2+B2+O)组织。随固溶温度的升高,初生板条状O相和等轴α_2相转变为B2基体相,B2相的体积分数逐渐增大。当固溶温度为1000℃时,B2相发生再结晶,出现了细小晶粒组织。固溶温度升高到1040℃时,晶粒明显长大,达200μm左右,且未溶解的初生α_2/O相也有所长大。油冷过程中,由于再结晶时间充分,晶粒变大。     

等温锻造温度对2B70铝合金组织性能的影响

研究了不同等温锻造温度对2B70铝合金显微组织与力学性能的影响.结果表明随着锻造温度的升高.2B70合金的室温拉伸性能变化不显著,在450℃达到峰值,在很宽的锻造温度范围保持了较好的塑性,最佳等温锻造温度为430～450℃.经等温锻造及固溶时效处理后,显微组织不具有明显的方向性,晶粒多为等轴晶,具有优良的组织均匀性和稳定性.在450～480℃,S(Al2CuMg)和Mg2Si等强化相析出明显增多,480℃时晶粒明显长大.     

不同热处理工艺对Ti-62222s钛合金棒材组织和性能的影响

研究了不同热处理工艺对Ti-62222s钛合金棒材显微组织和力学性能的影响。结果表明：Ti-62222s合金在两相区经过普通退火处理后,随着退火温度的升高,初生α相尺寸略有增加,β转变组织增多,次生α片层厚度增加,具有较好的塑性;而经过两相区固溶+时效处理得到双态组织,通过控制固溶温度以及时效温度来调整初生α相含量以及次生α片层厚度,以改善其强度、硬度和塑性。采用880℃/1 h/AC+540℃/8 h/AC两相区固溶+时效的热处理工艺,可实现合金强度-塑性-硬度的较好匹配,获得优良的综合性能。     

Ti2AlNb合金近β等温锻造组织与性能研究

对成分为Ti-22Al-25Nb(at%)的Ti2AlNb合金在近β等温锻造与锻后热处理过程中的组织转变规律及其对力学性能的影响进行了研究。结果表明,经近β等温锻造/空冷后,合金获得由少量均匀分布的α2相等轴颗粒和转变B2相基体(基体中含有排列杂乱的细小O相板条)构成的双态组织。锻后经960℃及其以上温度处理/水冷的合金再经时效处理后,依然具有双态组织;而经940℃及其以下温度处理/水冷的合金再经时效处理后,则获得由少量均匀分布的α2相等轴颗粒、粗大和细小两种尺寸的O相板条以及B2相基体构成的三态组织。三态组织中的粗大板条造成合金的强度有所下降,但塑性、持久、断裂韧性和疲劳性能均有不同程度的提高,其各项力学性能的匹配好于双态组织。     

β锻造Ti-22Al-25Nb合金的组织转变与拉伸性能

采用SEM等方法观察经β相区温度锻造的Ti-22Al-25Nb合金在β相转变点以下不同热处理过程中的微观组织转变,测试所得组织状态下的合金拉伸性能。对该合金的微观组织转变规律以及与拉伸性能的关系和机理进行分析。结果表明,在固溶处理过程中,组织中原有的α2相颗粒和O相板条因溶解而减少,B2相基体含量相应增大;固溶处理温度升高可加剧各相含量的变化趋势,并在这一过程中伴随着B2相的再结晶且α2相和O相的存在对B2相的再结晶有限制作用;在时效过程中,O相以细小二次板条形式从B2相基体中析出,或在残留的α2相颗粒周边以块状形式生成。该合金经不同固溶＋时效处理后均具有良好的室温及高温拉伸性能;且因固溶温度升高造成细小O相二次板条含量增多而使合金呈强度升高、塑性下降的趋势,其中以1000℃固溶＋800℃时效处理的状态具有强度和塑性的最佳匹配。     

等温锻造Ti-22Al-25Nb合金的显微组织与力学性能

对Ti-22Al-25Nb(at%)合金在不同相区等温锻造与锻后热处理过程中的组织演变及其对力学性能的影响进行了研究。结果表明,在980℃(B2+α_2+O三相区)、1040℃(α_2+B2两相区)以及1060℃(B2相区)等温锻造并热处理之后,合金的显微组织表现为典型的等轴组织、双态及双尺寸的板条组织,各相的尺寸以及体积分数可以通过热处理制度来控制。合金的力学性能测试表明:双尺寸的板条组织具有较高的室温强度但塑性最低,而等轴组织具有较高的塑性,强度最低。等轴组织的抗蠕变性能最低,双态组织以及双尺寸的板条组织具有相似的抗蠕变性,后两种组织主要以板条组织为主导,板条组织具有比等轴组织更优异的抗蠕变性能。     

热喷涂TiB2-Ni复合涂层组织结构和力学性能

采用团聚烧结方法制备TiB₂-Ni复合粉末喂料,并采用大气等离子喷涂和高速火焰喷涂两种喷涂方法制备了TiB₂-Ni涂层,比较分析了两种涂层的显微组织、物相组成、孔隙率、硬度和断裂韧性.结果表明,与等离子喷涂相比,高速火焰喷涂制备的TiB₂-Ni涂层具有更高的致密度,TiB₂含量,硬度和断裂韧性.两种涂层中TiB₂都没有发生明显的脱硼,氧化,但等离子喷涂过程中TiB₂向金属相中发生了溶解生成了大量脆性Ni₂₀Ti₃B₆相,并降低了涂层中TiB₂的含量,这是涂层硬度和断裂韧性相对较低的主要原因.     

Microstructural and mechanical evaluation of Al-TiB2 nanostructured composite fabricated by mechanical alloying

Production of bulk Al-TiB₂ nanocomposite from mechanically alloyed powder was studied. Al-20 wt.% TiB₂ metal matrix nanocomposite powder was obtained by mechanical alloying (MA) of pure Ti, B and Al powder mixture. A double step process was used to prevent the formation of undesirable phases like Al₃Ti intermetallic compound, which has been described in our previous papers. The resultant powder was consolidated by spark plasma sintering (SPS) followed up by hot extrusion. The structural characteristics of powder particles and sintered samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness measurements were conducted on the cross section of powder particles and sintered sample and the tensile behavior of extruded samples was evaluated. The results showed that the prepared Al-20 wt.% TiB₂ nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20 wt.% TiB₂ showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively, which are much higher than those reported for similar composites made by other processes.     

Phase transition and mechanical properties of ZrNxOy thin films on AISI 304 stainless steel

ZrN_xO_y thin films were deposited on AISI 304 stainless steel (304SS) substrates by reactive magnetron sputtering. The specimens were produced by sputtering a Zr target at 500 °C and the reactive gasses were N₂ and O₂ at various flow rates (ranging from 0 to 2 sccm). The purpose of this study was to investigate the effect of oxygen flow rate on the phase transition and accompanying mechanical properties of the ZrN_xO_y thin films. The oxygen contents of the thin films increased significantly with increasing oxygen flow rate. X-ray diffraction (XRD) revealed that the characteristics of the films can be divided into three zones according to the major phase with increasing oxygen content: Zone I (ZrN), Zone II (Zr₂ON₂) and Zone III (m-ZrO₂). The hardness of the ZrN_xO_y films decreased with increasing oxygen content due to the formation of the soft oxide phase. Modified XRD sin²ψ method was used to respectively measure the residual stresses of ZrN, Zr₂ON₂ and m-ZrO₂ phases. The results showed that the residual stress in ZrN was relieved as the oxygen content increased, and Zr₂ON₂ and m-ZrO₂ were the phases with lower residual stress. Compositional depth profiles indicated that there was a ZrO₂ interlayer near the film/substrates interface for all samples except the mononitride ZrN specimen. Contact angle was used as an index to assess the wettability of the film on substrate. The contact angles of ZrN, Zr₂ON₂ and m-ZrO₂ on stainless steel were indirectly measured using Owens-Wendt method. The results showed that ZrO₂ possessed the lowest wettability on 304SS among the three ZrN_xO_y phases, indicating that the ZrO₂ interlayer may account for the spallation of the ZrN_xO_y films after salt spray tests.     

Structure and mechanical properties of plasma sprayed nanostructured alumina and FeCuAl-alumina cermet coatings

Nanostructured alumina (Al₂O₃) and nanostructured cermet coatings containing alumina dispersed in a FeCu or FeCuAl matrix, were deposited by atmospheric plasma spraying (APS) from nanostructured powders. These coatings were characterized by SEM, EDAX, TEM, XRD and nanoindentation. Friction and wear behaviour were investigated by sliding and abrasion tests. TEM and XRD revealed that a nanostructuring was retained in the APS deposited coatings.The nanostructured ceramic and cermet coatings were compared in terms of coefficient of friction and wear resistance. Nanostructured cermet coatings appeared to offer a better wear resistance under sliding and abrasion tests than nanostructured Al₂O₃ coatings. The role of Fe, Cu, and Al additions to the Al₂O₃ coatings on friction and wear behaviour, was investigated.In the case of FeCu- and FeCuAl-based cermet coatings containing alumina, though the starting material consist of only two compounds, the coatings contain up to four different phases after plasma spraying. The mechanical properties of these different phases namely crack sensitivity and elasto-plastic deformation was determined by nanoindentation. The failure mechanisms were investigated and an attempt was made to establish a ‘structure-property’ relationship. It was shown that an appropriate balance between hard and soft phases results in optimum tribological properties of the nanostructured cermet coatings.     

Thermoelectric properties of tin-filled skutterudites prepared by mechanical alloying process

Sn-filled (Fe, Co)Sb₃ skutterudites of the form of Sn_yFe₃Co₅Sb₂₄ (0≤y≤1.5) were synthesized by the mechanical alloying of elemental powders followed by vacuum hot pressing. The phase transformations that occur during both mechanical alloying and vacuum hot pressing were examined by X-ray diffraction. Single-phase Sn-filled skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. The thermoelectric properties of the hot-pressed specimens were evaluated as a function of temperature and tin content. The void filling of tin (up to y=1.0) in Fe₃Co₅Sb₂₄ appeared to increase the thermoelectric figure of merit.     

Effects of Pd concentration on the interfacial reaction and mechanical reliability of the Sn-Pd/Ni system

The liquid-solid reaction between Sn-xPd alloy and Ni (x = 0.05-1 wt.%) and the resulting mechanical reliability of the system were examined in this study. The reactions strongly depended on the Pd concentration and the reaction time. When the Pd concentration was low (i.e., x = 0.05 wt.%), the reaction product was only Ni₃Sn₄. In contrast, when the Pd concentration was high (i.e., x ≥ 0.2 wt.%), the reaction product became a dual-layer structure of (Pd,Ni)Sn₄-Ni₃Sn₄. Between 0.05 wt.% and 0.2 wt.% (e.g., x = 0.1 wt.%), discontinuous (Pd,Ni)Sn₄ grains scattered over the Ni₃Sn₄ layer developed. Interestingly, the (Pd,Ni)Sn₄ grains were gradually dispersed in the molten Sn-Pd alloy, leaving the Ni₃Sn₄ at the interface, as the reaction time increased. These Pd-dependent reactions were dictated by thermodynamics and can be rationalized using the Pd-Ni-Sn isotherm. Furthermore, the results of the high-speed-ball-shear (HSBS) test indicated that the mechanical strength of the Sn-Pd/Ni joints dramatically degraded by over one third due to the formation of (Pd,Ni)Sn₄ at the interface. The implication is that the Pd concentration in Sn-Pd solder joints should be reduced to a level below 0.2 wt.% to prevent the creation of an undesired microstructure.     

Environmental effect on mechanical properties of aluminide matrix composites

This paper investigates the validity of the toughness measurement with a variation of the loading rate for distinguishing the fracture mechanism of aluminide intermetallics and their composites. The ductility and fracture toughness of Ni₃Al alloys and their composites are governed by inherent grain boundary brittleness and moisture-induced embrittlement at ambient temperatures. Although B doping is effective in suppressing both factors, remarkable improvement of toughness mainly depends on grain boundary strengthening. The toughness of the alloys is influenced by the dislocation locking mechanism and the extrinsic embrittlement promoted by diffusion of oxygen at intermediate temperatures. Extrinsic embrittlement is the predominant mechanism in determining the toughness at 673 K. Restriction of the dislocation motion is the predominant factor in determining toughness at 873 and 1073 K. The composites reinforced with TiC particles exhibit exceptionally constant toughness at 300 to 900 K.     

Structural, mechanical and tribological properties of Mo-S-C solid lubricant coating

Mo-S-C self-lubricating coatings were deposited by d.c. magnetron sputtering from carbon and molybdenum disulphide targets. The power ratio of the targets was varied in order to prepare films with carbon content in the range 0-55 at.%. Whatever the carbon content, the S/Mo ratio was higher than 1.25. The hardness of the films increased almost linearly with the carbon content. X-ray photoelectron spectroscopy showed evidence of Mo-C bonds; nevertheless, the size of molybdenum carbide grains was expected to be very small, since X-ray diffraction did not reveal any peaks related to any Mo-C phase. The coatings tested by pin-on-disc exhibited low friction, decreasing with increasing carbon content, when humid air was present. In nitrogen, the friction of all films was lower than 0.02 except for the reference MoS₂ (0.04). Mo-S-C outperformed the wear resistance of MoS₂; on the other hand, the results were in some cases hindered by the low adhesion of the coatings. The films were very sensitive to air exposure leading to surface oxidation.     

Influence of process control agent on interdiffusion between Al and Mg during mechanical alloying

The influence of a process control agent (PCA) on the reaction rate during mechanical alloying has been studied. Mechanical alloying of Al–Mg powder mixtures with different PCAs was carried out using a planetary ball mill. X-ray diffraction spectra showed that a small amount of PCA might lead to fast interdiffusion and reaction between Al and Mg although the crystalline sizes were in general the same for the powders when using different amounts of PCA. The fast interdiffusion and advanced reaction are closely associated with the diffusion distance between the powder particles due to the presence of PCA and to the actual weight ratio of ball to powder.     

Interfacial reaction in ASZ/A384 Al composite and its influence on mechanical properties

In an ASZ/A384 Al composite, the interfacial reaction was observed to take place between the SiO₂ binder layer and Mg within the matrix to form MgAl₂O₄ at the interface. Formation of MgAl₂O₄ at the interface between ASZ short fibers and the Al matrix alloy is believed to enhance the interfacial bonding strength, resulting in improved composite strength. However, the interfacial reaction in the ASZ/A384 Al proceeds at the expense of Mg in the matrix, resulting in a composite devoid of Mg bearing precipitates such as Al₂CuMg and Mg₂Si.