Properties of (Ti,Nb)Al–(Ti,Nb)5Si3 eutectic composite

Ti–40Al–5Si and Ti–39Al–5Si–2Nb (in at.%) alloys were studied as prospective high-temperature structural composites consisting of γ-(Ti,Nb)Al + α₂-(Ti,Nb)₃Al matrix and Ti₅Si₃ reinforcement. The alloys were prepared by arc melting under helium. Oxidation resistance was studied at 900 °C in air. Thermal stability of alloys was investigated by measuring room temperature hardness and compressive strength after long-term annealing at 900 °C. To prepare oriented composites, directional crystallization at rates of 5–115 mm/h was carried out by the floating zone technique. It was observed that the addition of 2% Nb to the Ti–40Al–5Si alloy does not modify eutectic structure. Niobium is almost uniformly distributed in all present phases. Both alloys show excellent oxidation resistance at 900 °C in air. The Nb-addition causes significant improvement of oxidation resistance due to the doping effect and increase of Al activity in the scales. Room temperature hardness and compressive strength of both as-cast alloys are similar – about 500 HV and 1600 MPa, respectively. Room temperature mechanical properties do not reduce significantly after 300 h annealing at 900 °C, due to a high morphological stability of eutectic silicides. Directionally solidified alloys consist of columnar Ti–Al grains elongated in crystallization direction and silicides. Niobium refines both Ti–Al grains and Ti₅Si₃ silicides. As a consequence, orientation and elongation of silicides in the Nb-containing alloy are reduced. In the Ti–Al–Si alloy directionally crystallized at 5–115 mm/h, the silicide interparticle spacing λ (in mm) is related to the crystallization rate R   (in mm/h) by a following expression: λ^1.33·R=0.32${\lambda }^{1.33}·R=0.32$. In the Nb-containing alloy, silicide interparticle spacing does not depend on the crystallization rate.     

Microstructures and mechanical properties of directionally solidified Ti–45Al–8Nb–(W,B, Y) alloys

Intermetallic Ti–45Al–8Nb–(W, B, Y) (at.%) alloys were directionally solidified at growth rates of 10–400 μm/s with a Bridgeman type apparatus. Microstructures and room temperature (RT) mechanical properties of the directionally solidified (DS) alloys were investigated. The microstructures with different segregation morphologies were observed at different growth rates. Fully lamellar (FL) microstructure evolves into a massive microstructure when the growth rate is up to 100 μm/s. Both the width of columnar grain and the interlamellar spacing decrease with increasing growth rate. Compressive properties were not proportional to the growth rates but closely related to the segregation morphologies. Only the DS alloy with columnar pattern of Al-segregation had tensile ductility. A better RT tensile plastic elongation level of 2% and yield strength 475 MPa were obtained at growth rate of 10 μm/s. Cracks propagated in transgranular mode predominantly. Larger elongated B2 particles produced in the interdendritic regions were detrimental to the tensile ductility of the DS alloy.     

Strain-induced precipitation kinetics of Nb(C,N) and precipitates evolution in austenite of Nb–Ti micro-alloyed steels

In this article, the precipitation–temperature–time (PTT) curves were obtained by plotting 1/A _r-time curves (A _r represents the area under the flow curves, and some details were clarified in the section “1/A _r method”) using two-stage interrupted compression testing. Based on the measured PTT curves, the L_J model has been applied to calculate the complete PTT curves by adjusting the modification factor, f, to be 0.022, from which it can be seen that they are both typical C-shaped with the nose temperature ranging from 900 to 925 °C. By using additivity rule, the continuous-cooling-precipitation (CCP) curves were established. And the critical cooling rates for precipitation start were also determined for different cooling start temperatures, and the effects of cooling rates and cooling start temperatures on CCP curves were systematically clarified. The evolution of precipitates was found to be in good agreement with PTT curves. Numerous fine and round precipitates were formed during holding after first compression deformation, which could have hindered static recrystallization kinetics and accounted for the plateaus on 1/A _r-time curves. In addition, The cubic precipitates are mainly undissoloved TiN-rich (Ti,Nb) (C,N) carbonitrides. And based on the CCP and continuous-cooling-transformation curves of tested steel, the effect of cooling paths on precipitation and transformation were also discussed in details.     

溅射(Ti,Al)N薄膜的机械性能

运用直流平面磁控反应溅射在抛光淬火的TSA碳素工具钢上沉积(Ti,Al)N薄膜。研究了反应气体N_2流量与基片偏压对形成(Ti,Al)N薄膜的显微硬度的影响。在N_2流量约为10sccm,P_(N2)/P_(Ar),约为0.12与偏压U_B=200V时,(Ti,Al)N薄膜的显微硬度接近极大,可达3000kgf/mm~2。(Ti,Al)N薄膜划痕实验的临界负载L_c约为31N。磨损实验表明,(Ti,Al)N薄膜比淬火的T8A碳素工具钢基底具有好得多的耐磨损特性。微观分析表明(Ti,Al)N薄膜具有良好的抗氧化性能是由于氧化过程中在薄膜表面形成Al-O保护层。     

(Al,Ti)N涂层力学性能工艺研究

通过磁控溅射离子镀与中频脉冲偏压电源相结合,优化制备(Al,Ti)N涂层的工艺。利用HVS-1000数显显微硬度计检测涂层硬度;MET-400多功能材料表面试验仪测定膜基结合力,JS-QHY-2型球痕仪测定厚度,DX-1000型X射线衍射仪检测物相。采用正交实验,作算术平均值和极差分析,优化制备涂层的工艺。结果表明波动时,最佳工艺为功率为10:24,脉冲偏压为100V,时间为2.5h,不波动时最佳工艺为5:24,脉冲偏压为100V,时间为2.5h。     

(Ti,Al, Cr)N膜系的研究进展

总结了(Ti,Al,Cr)N膜系的沉积方法并讨论了化学成分、N2流量以及基底偏压等工艺参数对薄膜产生的影响,针对(Ti,Al,Cr)N膜系的相组成与膜层成分、抗氧化性、耐腐蚀性、显微硬度、抗摩擦磨损性能以及膜基结合力等方面进行了详细阐述.在此基础上,对(Ti,Al,Cr)N膜系的未来发展进行了展望,以期为多组元氮化物硬质膜的研究提供参考.     

Al含量对(Ti,Al)N涂层结构性能的影响

(Ti，A1)N是20世纪80年代末期在TiN基础上发展起来的一种新型多元涂层材料。由于加入Al元素，(Ti，Al)N不但硬度、耐磨性优于TiN，而且大大改善了涂层的抗高温氧化性能。综述了Al元素在(Ti，Al)N涂层中的作用机理，以及Al含量对(Ti，Al)N涂层的晶体结构、抗高温氧化、硬度和耐磨性的影响。指出当Ti和Al的比例近似为1：1时，(Ti，Al)N涂层将获得优越的综合使用性能。     

直流磁控溅射制备(Ti,Al)N薄膜研究

本研究采用直流磁控溅射的方法在W 18Cr4V高速钢基体上制备不同Al/Ti比例的(Ti,Al)N薄膜,为此,在圆柱形磁控溅射Ti靶表面上,采用多弧离子镀技术覆盖不同面积和一定厚度的纯Al,结果表明:只有在靶材的外表面Ti与Al的交界附近的样品才能沉积成薄膜,随着靶材表面覆盖纯A l的面积增大,所形成的结晶薄膜中的Al/Ti比例增大,膜层中的相组成AlN的数量增多,而TiAlN的数量减少,此外纯Al的覆盖面积过大,将导致溅射时所需要的气压过高而无法沉积成膜。     

Mechanical properties of Ir–Nb–Pt–Al quaternary alloys

Ir–Nb–Pt–Al quaternary alloys had exhibited suitable microstructure for high-temperature usage in the previous study. In this work, investigations were made of the mechanical properties of these quaternary alloys. Compression tests at 1200 °C were carried out for five samples, and compression creep test at 1400 °C under 100 MPa was conducted for one sample. These alloys showed high strength and good creep resistance.     

Solid state phase transformations in Ti–Al–C and Ti–Al–Nb–C alloys

Abstract

Results are reported of an investigation of solid state transformations in a series of α₂ based alloys having an aluminium content of 26 at.-% with carbon up to 3 at.-%; two α₂ basedquaternary Ti–Al–Nb–C alloys with 5 and 12 at.-%Nb and 3 at.-%C were also studied. Ordering occurs in the ternary Ti–Al–C alloys and also in the 23Al–5Nb–3C alloy on quenchingfrom 1250°C. Additional carbide precipitation was not observed in the ternary Ti–Al–C alloys on reheating to 750°C. Additions of niobium resulted in the presence of the β phase at 1050°C in the 5%Nb alloy and at 1050 and 750°C in the 12%Nb alloy. In the quaternary Ti–Al–Nb–C alloys, (Ti, Nb)₃AlC was found to be the primary phase and was present in the microstructure over the temperature range studied. In the 21Al–12Nb–3C alloy, the ordered β phase transformed to α″₂ martensite on quenching from 1250;amp;#x00B0;C.

MST/1306     

Phase composition,structure, and mechanical properties of arc PVD Mo–Si–Al and Mo–Si–Al–N coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al coatings with a uniform distribution of equiaxed grains 8–12 nm in size and Mo–Si–Al–N coatings with a multilayer structure and a modulation period from 22 to 25 nm. The former coatings consist of MoSi₂ and Mo and the latter consist of Mo2N and amorphous Si₃N₄ and AlN. The hardness of the Mo–Si–Al–N and Mo–Si–Al coatings is 41 and 18 GPa, respectively; they are similar in resistance to elastic deformation; and the Mo–Si–Al–N coating has a considerably higher resistance to plastic deformation. The coatings have roughly identical coefficients of friction (~0.67–0.69 at 20°C and ~0.52–0.56 at 550°C), but the wear resistance of the Mo–Si–Al–N coating is higher by three and two orders of magnitude at 20 and 550°C, respectively. The coatings of the two systems exhibit good adhesion to the substrate and cohesive fracture. Partial wear of the Mo–Si–Al and Mo–Si–Al–N coatings in the course of scratch testing occurs at indentation loads of 80 and 63 N, respectively.     

(Zr,Al)N薄膜的微结构及性能研究

采用射频磁控反应溅射在单晶Si(100)上沉积了一系列不同Al含量的(Zr,Al)N薄膜,利用能谱仪(EDS)、X射线衍射仪(XRD)、扫描电镜(SEM)和微力学探针对薄膜的成分、结构、力学和抗氧化性能进行了表征。研究结果表明,当Al含量在0%~20.31%(原子分数)之间时,薄膜是B1型(NaCl)单相结构;当Al含量为31.82%时,同时出现B1和B4型(ZnS)双相结构。当Al含量超过36.82%时,以B4结构为主。随着铝含量的增加,薄膜晶面间距减小,晶格常数变小。薄膜的力学性能测试表明,适当的Al含量可以提高薄膜的硬度。随着Al含量的增加,薄膜的抗氧化性能得到改善,对于B1型(Zr,Al)N薄膜,其结构稳定性也得到增强。     

(Ti,Al)N薄膜的升温出气特性研究

介绍了采用多弧离子镀方法在不锈钢表面镀覆(Ti,Al)N薄膜,并对膜的结构、表面成分和形貌进行了简单分析,用热出气方法研究其出气特性,并与不锈钢的热出气性能进行比较,发现在不锈钢表面镀覆一层(Ti,Al)N膜可以有效地阻挡不锈钢体内氢扩散和碳偏析,因此(Ti,Al)N是比较理想的真空材料。     

射频磁控溅射(Ti,Al)N薄膜性能的研究

采用射频磁控溅射，用Al靶和Ti靶同时溅射沉积（Ti，Al）N薄膜。研究表明：不同Al靶功率沉积的薄膜中始终存在面心立方结构（B1型），当Al靶功率大于250W薄膜中面心立方结构（B1型）和六方结构（B4型）共存。随Al成分的增加，B1型结构晶格常数减小，薄膜择优取向由B1型（111）向B4型（002）转变。薄膜表面随Al靶功率增加分别呈岛状、纤维状和柱状增长。（Ti，Al）N薄膜的硬度随Al靶功率的增加呈上升趋势。等离子体发射光谱分析显示，在相同工艺条件下Al靶比Ti靶先进入非金属态溅射模式，导致在相同功率下Al溅射速率低于Ti溅射速率。     

Hot ductility of directly cast C–Mn–Nb–Al steel

Abstract

Tensile samples of a C–Mn–Nb–Al steel (BS 4360: 50D grade) have been cast in situ and either directly tested in the temperature range 850–1200°C, or were allowed to cool through the transformation, re–solution treated, and then tested in the same temperature range. The hot ductility of the directly tested cast material was found to be superior to that of the reheated material. Carbon extraction replicas taken close to the fracture surfaces showed large differences in the distribution of sulphide inclusions and NbCN precipitates along the γ boundaries. The directly cast material had sulphide inclusions and NbCN precipitates present in the form of coarse particles situated close to the interdendritic boundaries. A significant proportion of these coarse sulphide inclusions and NbCN eutectics, produced during solidification, redissolved on reheating at 1330°C, and subsequently precipitated in a much finer form at the γ grain boundaries, reducing hot ductility. It appears likely that the very marked segregation which occurred during solidification enhanced the interdendritic regions with sulphur to such an extent that the sulphideformed was (Mn, Fe)S, which in gradually changing to the equilibrium precipitate, depleted the surrounding matrix of manganese. The low manganese level accompanying these inclusions allowed a greater degree of solution of the sulphides to occur on reheating and accounted for the subsequent fine precipitation at the boundaries.

MST/361     

Thermodynamic characterization of Al–Cr,Al–Zr,and Al–Cr–Zr alloy systems

Abstract

The equilibrium phase diagrams of Al–Cr, Al–Zr, and Al–Cr-Zr, with particular reference to aluminium-rich alloys, have been critically reviewed. On the basis of these, and consistent with measured thermodynamic values, the binary systems have been thermodynamically characterized. Using these characterizations, phase equilibria have been extrapolated in the ternary, with the intention of augmenting the sparse experimental information concerning the equilibrium liquidus (0–10 at.%Cr, Zr) and solid solution range of aluminium in Al–Cr–Zr. Using the same parameters that define the equilibrium phase relationships, metastable phase relationships can also be extrapolated into the ternary.

MST/418     

Nb,Zr添加量对粉末烧结Nd(Dy,Gd)-Fe(Nb,Zr,Al,Cu)-B晶界相形成和矫顽力的影响

制备了复合添加0.8%(原子分数)Nb+0.9%(原子分数)Zr和复合添加1.5%(原子分数)Nb+1.2%(原子分数)Zr的两种粉末烧结Nd(Dy,Gd)Fe(Nb,Zr,Al,Cu)B永磁体,通过对它们的微观结构、微区成分以及磁性能的分析,研究了Nb、Zr添加量对磁体晶界相形成的影响以及晶界新相与磁体矫顽力之间的关...     

Microstructure and precipitation in Al–Li–Cu–Mg–(Mn,Zr) alloys

Abstract

Hot rolled Al–6Li–1Cu–1Mg–0·2Mn (at.-%) (Al–1·6Li–2·2Cu–0·9Mg–0·4Mn, wt-%) and Al–6Li–1Cu–1Mg–0·03Zr (at.-%) (Al–1·6Li–2·3Cu–1Mg–0·1Zr, wt-%) alloys developed for age forming were studied by tensile testing, electron backscatter diffraction (EBSD), three-dimensional atom probe (3DAP), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). For both alloys, DSC analysis shows that ageing at 150°C leads initially to formation of zones/clusters, which are later gradually replaced by S phase. On ageing at 190°C, S phase formation is completed within 12 h. The precipitates identified by 3DAP and TEM can be classified into (a) Li rich clusters containing Cu and Mg, (b) a plate shaped metastable precipitate (similar to GPB2 zones/S″), (c) S phase and (d) δ′ spherical particles rich in Li. The Zr containing alloy also contains β′ (Al₃Zr) precipitates and composite β′/δ′ particles. The β′ precipitates reduce recrystallisation and grain growth leading to fine grains and subgrains.     

Structure,Composition, and Properties of Arc PVD Mo–Si–Al–Ti–Ni–N Coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al–Ti–Ni–N coatings with a multilayer architecture formed by Mo₂N, AlN–Si₃N₄, and TiN–Ni and a crystallite size on the order of 6–10 nm. We have studied the physicomechanical properties of the coatings and their functional characteristics: wear resistance, adhesion to their substrates, and heat resistance. According to high-temperature (550°C) wear testing and air oxidation (600°C) results, the coatings studied here are wearand heat-resistant under appropriate temperature conditions. Their properties are compared to those of Mo–Si–Al–N coatings.