Ti、B复合细化对高温铸造铝合金（ZL－208）的作用

Ｔｉ、Ｂ复合细化使ＺＬ－２０８高温铸造铝合金的高温持久性能受到损害，对室温拉伸和疲劳性能作用不明显。：取６炉１８根试样算数均值。图３　Ｔｉ、Ｂ复合细化对合金高温持久破断寿命的影响（３００℃、８８．３ＭＰａ；３－５炉数据）复合细化剂中的Ｔｉ是合金成分之一，总含量符合技术条件要求［４］，只有Ｂ是新添加的微量元素，与Ａｌ、Ｔｉ等形成Ｂ化物质点［１］，有可能是残存在合金中的这些质点或以其它形式存在的Ｂ损害了高温性能。（３）疲劳性能疲劳性能采用φ４×２５ｍｍ光滑试样在Ｅ型／１００００转／分，循环周次为２×１０７条件下测试，用沉降法求出室温和３００℃未细化和复合细化的疲劳强度，结果列入表２。表２表明Ｔｉ、Ｂ复合细化后的合金室温和高温疲劳性能没有明显变化，这可能是由于复合细化使合金晶粒度减小有限所致。表２　Ｔｉ、Ｂ复合细化对合金疲劳性能的影响３．３铸件切取性能为了进一步验证Ｔｉ、Ｂ复合细化的作用，对未经Ｔｉ、Ｂ复合细化的某直升机发动机附件—减速器机匣前部铸件，与同种经Ｔｉ、Ｂ复合细化的铸件（法国产）进行切取性能对比试验，切取试样直径为φ３，两铸件的化学分析成分列入表３。切取性能对比试验结果如表４、表５所示。表４表明两种铸     

微量元素B对Ti-48Al合金组织细化的影响

研究了微量元素Ｂ对Ｔｉ－４８Ａｌ合金组织细化的作用。结果表明：加入微量Ｂ可在合金中生成细长的带状ＴｉＢ２相。Ｂ含量达０．８ａｔ％时,可显著细化铸态组织：１１５０℃／ｈ／ＡＣ处理时,除晶界外,含Ｂ合金中的７相还可以从ＴｉＢ２基体界面上形核析出,因形核部位的增加,细化了近γ组织,在α单相区热处理,ＴｉＢ２相可非常有效地阻碍α晶粒长在,加入０．５ａｔ％Ｂ可使全片层组织平均晶粒直径降低一个数量级。     

高温退火和时效处理对Ni47Ti44Nb9合金显微组织和马氏体相变的影响

本文用金相显微镜，电子探针和电阻率－温度曲线测试仪研究了高温退火和时效对Ｎｉ４７Ｔｉ４４Ｎｂｇ合金显微组织和马氏体相变的影响。结果表明，加热温度高于１０５０℃时，β－Ｎｂ相粒子聚集长大，但对马氏体相变并不产生明显影响。与富Ｎｉ的近等原子比Ｔｉ－Ｎｉ合金不同，Ｎｉ４７Ｔｉ４４Ｎｂｇ合金在时效过程中没有时效析出和时效硬化现象。Ｎｂ加入Ｔｉ－Ｎｉ合金中抑制了时效析出和Ｒ相变，从而降低了马氏体相变温度受热     

TiAl基合金中的不连续粗化转变

为细化铸造ＴｉＡｌ基合金的显微组织,将成分为Ｔｉ－４４．９Ａｌ、Ｔｉ－４８Ａｌ以及Ｔｉ－４４．３Ａｌ－３．０Ｃｒ（ａｔ％）的三种合金在略高于Ｔｉ－Ａｌ共析温度的１１５０℃进行长时保温处理。结果表明,保温一定时间后,合金中的Ｔｉ３Ａｌ＋ＴｉＡｌ片层组织会发生三种类型的不连续粗化转变,转变结果均能在一定程度上细化合金的铸态晶粒尺寸,其中Ｔｉ－４４．３Ａｌ－３．０Ｃｒ合金的晶粒细化效果最佳。此外,Ａｌ含量的增加,合金元素Ｃｒ的加入等都会大大促进合金的不连续经转变过程。     

颗粒增强TiAl基复合材料及其Si的韧化作用研究EI

运用ＸＤ工艺制备了颗粒增强ＴｉＡｌ基复合材料。增强颗粒均匀分布于ＴｉＡｌ基体中并细化ＴｉＡｌ合金。通过在ＴｉＢ_２／ＴｉＡｌ、ＴｉＣ／ＴｉＡｌ复合材料中加入适量的Ｓｉ，颗粒增强ＴｉＡｌ基复合材料的室温延性得到了改善。     

TiAl及TiC／TiAl合金的XD合成研究

本文研究了用ＸＤ工艺合成ＴｉＡｌ合金及ＴｉＣ／ＴｉＡｌ复合材料，研究结果表明，可在Ａｌ的熔点附近用ＸＤ工艺制备ＴｉＡｌ合金及其ＴｉＣ颗粒增强复合材料。ＴｉＡｌ合金由ＴｉＡｌ＋Ｔｉ３Ａｌ相组成，而ＴｉＣ／ＴｉＡｌ复合材料由ＴｉＣ＋ＴｉＡｌ＋Ｔｉ３Ａｌ相组成。     

铝钛晶粒细化合金的离心压力铸造及其细化效果

研究了高钛晶粒细化中间合金的制造法以及它对铝合金的作用效果。试验结果表明，由于浇组时旋转离子压力作用，使铝钛合金细化剂中的Ａｌ３Ｔｉ颗粒明显减小，因而可使细化剂中允许的钛含量提高将近４倍，这样可大大减小细化剂在在被处理合金中的加入量。     

微量稀土元素铈和钕对TiNi合金马氏体相变的影响

本文利用Ｘ射线衍射、光学显微镜、透射电镜和电阻测量方法，研究了微量稀土元素铈和钕对近等原子比ＴｉＮｉ合金马氏体相变的影响，结果表明，加入稀土元素Ｃｅ和Ｎｄ细化了ＴｉＮｉ合金晶粒，提高了马氏相相变点。稀土元素Ｃｅ使合金经时效处理后，其Ｒ相变与马氏体相变分离开，并使合金相变滞后变窄。     

Ti,B复合细化对高温铸造铝合金（ZL—208）的作用

Ｔｉ、Ｂ复合细化使ＺＬ－２０８高温铸造铝合金的高温持久性能受到损害，对室温拉伸和疲劳性能作用不明显。     

Ti合金基复合材料精细结构

用ＪＥＭ２０００ＥＸＩＩ高分辨电子显微镜（ＨＲＥＭ）研究了ＴｉＢ晶须增强的Ｔｉ合金基复材料的精细结构。分析了ＴｉＢ晶须的生长形貌和堆垛层错，β－Ｔｉ的超结构及ＴｉＢ和Ｔｉ合金基体界面。测定了α－Ｔｉ或β－ＴｉＢ的取向关系。     

High Manganese Steel Alloying Process and Its Influence on Microstructure and Properties of the Steel

The influence of two kinds of alloying processes, adding Nb (or Ti) and N-Mn alloy as well as adding Nb (or Ti) and spraying N2, on microstructures and properties of a high manganese steel has been studied. It has been found that adding Nb(or Ti), accompanying with N-Mn alloy, is unfavourable to microstructure compactness of the high manganese steel, but adding Nb (or Ti)and spraying N2 into the melt is good for refining austenitic grain, forming a lot of hard particles and improving microstructure compactness. The mechanical properties of the high manganese steel have relation to the content of elements Nb or Ti. Its fracture mode will turn ductile fracture into brittle cleavage fracture gradually. By X-ray and TEM analysis, it is proved that the austenite can be transformed to deformation-induced α martensite after adding a certain amount of element Nb (or Ti). The microstructure transformation of alloying high manganese steels through deformation is one of methods for strengthening austenite matrix and increasing the work-hardening rate as well as improving antiwear property.     

Al-5Ti-1B对A357合金晶粒细化作用的研究

采用Al-5Ti-1B中间合金作为细化剂细化A357合金,考察细化剂加入量、保温温度及熔体在不同温度下保温时间对晶粒尺寸的影响,研究了Al-5Ti-1B中间合金对A357合金晶粒细化效果.研究表明:Al-5Ti-1B可明显减小A357合金的晶粒尺寸,并且在较长的时间内保持良好的细化效果;熔体长时间静置后易出现(钛)偏析,底部Ti含量比顶部要高,致使铸件整体细化效果大大降低;定期对熔体进行搅拌可有效消除偏析.     

First-principles investigation of B2 partial disordered structure,martensitic transformation,elastic and magnetic properties of all-d-metal Ni-Mn-Ti Heusler alloys

In this work,the B2 partial disordered structure of the austenitic parent phase,martensitic transformation,elastic and magnetic properties of the Ni8 Mn4+xTi4-x(x=0,1 and 2) Heusler alloys have been systematically investigated by the first-principles calculations.The preferential atomic occupation of B2 structure is one Ti atom exchange with the nearest neighboring Mn atom from the view of lowest energy principle.This disordered exchange sites(Mn-Ti) and the excess Mn atoms occupying the Ti sites(MnTi)could reduce the nearest Mn-Mn distance,resulting in the anti ferromagnetic state in the austenitic and martensitic phases of the alloys.The total magnetic moment of the alloy decreases with the increasing Mn content;it is ascribed to the antiferromagnetic magnetic moments of the excess Mn atoms.When x=0,the alloy does not undergo martensitic transformation since the austenite has absolute phase stability.The martensitic transformation will occur during cooling process for x=1 or 2,owing to the energy difference between the austenite and the martensite could provide the driving force for the phase transformation.The elastic properties of the cubic austenitic phase for the Ni2 MnTi alloy is calculated,and the results reveal the reason why Ni-Mn-Ti alloy has excellent mechanical properties.The origin of martensitic transformation and magnetic properties was discussed based on the electronic density of states.     

Microstructure Evolution of Rapidly Solidified Ti_3Al-2Nb Alloy

It has been found from the analysis of X-ray diffraction and the observation of TEM that the metastable ordered orthorhombic martensite phase in the rapidly solidified Ti3Al-2Nb alloy transforms to various phases at different aging temperatures. When the alloy aged at temperature of 500℃ for 20 min, the phase decomposition into B2 and O phases is related to the stressin the alloy. When the aged temperature above 600℃, the phase transforms to α2 phase by both shearing and chemical ordering     

Microstructural evolution during fabrication of ultrafine grained alpha+beta titanium alloy

Abstract

In this work, several important problems related to the fabrication of ultrafine grained UFG alpha+beta titanium alloys have been investigated, taking Ti-6.5Al-3.3Mo-1.8Zr-0.26Si wt- as the model material. It has been shown that UFG titanium alloys can be produced by deformation at relatively low temperatures or high strain rates. There were different Zenner-Holloman parameter-grain size relationships in the relatively high temperature region 750-920C and the relatively low temperature region 650-750C for the present titanium alloy. During the compression of a martensite microstructure at 890C, both the alpha and beta phases were dynamic recrystallised and the lamellae were broken up by means of grain boundary sliding and phase penetration along the subgrain boundaries. During compression at 650C, alpha phases were dynamically recrystallised, and beta phases precipitated and grew in the matrix of alpha phases. It was suggested that the martensite microstructure should be preferred to other lamellar microstructures for the fabrication of UFG Ti alloys. The UFG Ti alloy demonstrated good superplasticity at relatively high strain rates and low temperatures.     

Fabrication of Ti–Nb–Ag alloy via powder metallurgy for biomedical applications

Ti and some of its alloys are widely used as orthopedic implants. In the present study, Ti–26Nb–5Ag alloys were prepared by mechanical alloying followed by vacuum furnace sintering or spark plasma sintering (SPS). The microstructure and mechanical properties of the Ti–Nb–Ag alloys were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX), compressive and micro-hardness tests. The effect of different sintering methods on the microstructure and properties of Ti–Nb–Ag alloy was discussed. The results showed that the titanium alloy sintered by vacuum furnace exhibited a microstructure consisting of α, β and a small amount of α″ martensite phase; whilst the SPS sintered alloy exhibited a microstructure consisting of α, β and a small amount of α″ martensite phase, as well as a nanostructured Ag homogeneously distributed at the boundaries of the β phases. The Ti–Nb–Ag alloy sintered by SPS possessed fracture strength nearly 3 times of the alloy sintered by vacuum furnace.     

Martensite formation in Ti–Allayers produced by laser surface alloying

Abstract

The microstructures of Ti–Al layers produced by laser surface alloying of a Ti substrate have been investigated for Al contents in the range 17–36 at.–%. The alloyed layers were obtained using a continuous wave CO₂ laser and a powder feed technique employing the following laser processing parameters: 1·8 kW power, 3 mm beam diameter, 7 mm s ^?1 traverse speed, and feedrates of Al powder ranging from 0·03 to 0·07 g s ^?1. The microstructures were disordered lath martensite α′ in 17 at.–%Al alloy, ordered massive and acicular martensite in 23 at.–%Al alloy, and ordered massive, acicular, and lath martensite in 30 and 36 at.–%Al alloys. The change in martensite type and morphology is discussed in relation to the available datafor the β to α′ transformation in Ti alloys.

MST/1437     

Structure and properties of ductile CuAlMn shape memory alloy synthesized by mechanical alloying and powder metallurgy

A ductile Cu–Al–Mn–Ti–B shape memory alloy with high fatigue strength has been prepared via mechanical alloying and powder metallurgy. With increasing milling time, the size of the crystallite grains decreases. Cu diffraction pattern appeared only after milling at a speed of 300 rpm for 25 h. The single phase CuAlMnTiB solid solution powder after 35 h milling was hot-pressed and extruded to form the final alloy. The quenched alloy had a single β phase at room temperature and its yield strength, maximum strength and strain were measured to be 390 MPa, 1015 MPa and 14.4%, respectively. The aged alloy showed a martensite structure at room temperature and had a shape memory recovery of 92% after 120 cycles.     

Influence of silicon and magnesium on grain refinement in aluminium alloys

Abstract

Grain refinement in Al–Si alloys with silicon contents in the range of 0·2–30 wt-% has been studied in detail with conventional as well as higher level additions of a Al–5Ti–1B master alloy. A poisoning effect was observed with Al–Si alloys containing ≥7 wt-%Si and the extent of poisoning increased with an increase in the silicon content. Silicon improves the grain refining behaviour of aluminium when added in small quantities (0·2%). Magnesium can counteract the poisoning effect of silicon. The optimum level of magnesium required to overcome the poisoning effect depends on the silicon content of the alloy. Higher level additions of a grain refiner could overcome the poisoning effect of silicon and the level required to achieve good grain refinement is a function of the silicon and magnesium contents of the alloy. The present paper also reports the influence of degasser and melt temperature on the grain refining response of Al–Si alloys.     

Influence of boron on the microstructure and mechanical properties of Al-11.6Si-0.4Mg casting alloy modified with strontium

Abstract

The influence of the addition of Al-1B master alloy on the microstructure and mechanical properties of Al-11.6%Si-0.4%Mg alloy modified with 0.030%Sr has been investigated. The mechanical properties and fracture behaviour of the alloys as cast and after T6 heat treatment with three different melt treatments (no treatment; 0.030%Sr modifying treatment; and 0.030%Sr + 0.028%B combined melt treatment) were also compared. Al-1B master alloy has a strong action in refining the dendritic structure in near eutectic Al-Si casting alloys modified with Sr. The Sr+B combined melt treatment can improve considerably the mechanical properties of the alloys, both as cast and after T6 heat treatment. Fracture modes of the alloys with the Sr modifying treatment and the Sr+B combined melt treatment are typically ductile. However, fractographs indicate that the alloy with combined melt treatment suffered greater ductile deformation before fracture. The Sr+B combined melt treatment significantly improves the mechanical properties of near eutectic Al-Si casting alloys.