定向凝固NiAl合金的拉伸行为研究

研究了定向凝固NiAl-Mo(Hf)和NiAl-Fe(Nb)合金的拉伸行为和显微组织变化.结果表明,两种合金在一定的拉伸条件下均具有反常的屈服行为和中温脆性.反常屈服和中温脆性行为与合金中含有的Ni3Al相有关.两种合金在高温时还表现出高应变速率的超塑性变形行为.超塑性变形的主要机理是位错滑移和攀移产生的应变硬化与动态回复和动态再结晶的应变软化作用相平衡.超塑性变形试样的断口呈韧性特征,在断裂区有孔洞产生.     

Mechanical Properties of DS NiAl/Cr(Mo) Alloys with Low Addition of Hf for High-temperature Applications

1.IntroductionAs a new type of structural materials based on the B2intermetallics,NiAl offers superior characteristics,suchas low density,high melting point and excellent oxida-tion resistance at high temperature[1].However,the poorfracture toughness at ambient temperature and low creepstrength at elevated temperature limit their applicationcurrently.Although the creep strength has been sig-nificantly improved by precipitation strengthening[2]orforming a particulate composite[3],and ductility…     

BDT and Creep Behaviors of NiAl-25 at. pct Cr Alloy at Various Temperatures

1.IntroductionIntermetallic compound of NiAl with B2crystal struc-ture is regarded as a potential candidate of high tem-perature structural materials because it offers attractivechemical and physical properties,such as high meltingpoint,low density,good thermal conductivity,high resis-tance to oxidation and high stiffness[1,2].Unfortunately,this kind of intermetallic compound shows limited tough-ness at ambient temperatures and poor strength at hightemperatures.An efficient way to prepare int…     

Microstructures and Creep Behavior of a Directionally Solidified NiAl-Fe(Nb) Multiphase Intermetallic Alloy

The microstrucure and creep behavior of a DS NiAl-Fe(Nb) multiphase intermetallic alloy have been investigated,This alloy exhibits dedritic structure ,in which dendritic arm is β-(Ni,Fe)(Fe,Al) phase surrounded by interdendritic region of γ′/γ phase ,The results of the creep test indicated that all of the creep curves have similar characteristic,which is a short primary creep stage and a dominant steady state crepp stage ,and the creep strain ranges from 18% to 52%,The apparent stress exponent and the apparent activation energy were analyzed and discussed,The mechanism of the creep deformation was also analyzed by the observation of TEM.     

Simultaneous improvement of strength and ductility in NiAl-Cr(Mo)-Hf near eutectic alloy by small amount of Ti alloying addition

Effects of Ti alloying addition on the microstructure and room temperature compression deformation behavior of a NiAl-Cr(Mo)-Hf near eutectic alloy were investigated by SEM, TEM, EDX and compression test. The results showed that compared with base alloy, the compressive fracture strain and 0.2% yield strength of the Ti-containing alloy were enhanced simultaneously. Disordered (Ti,Hf) solid solution phase together with the blocky Heusler phase Ni₂Al(Ti,Hf) precipitation presented at eutectic cell boundaries is responsible for the enhancement in ductility due to the better deformation ability of (Ti,Hf) solid solution phase. The improvement in strength depends mainly on the solid solution strengthening in NiAl matrix by large amount of Ti due to its larger solid solubility relative to Hf in NiAl.     

7B04铝合金超塑性变形行为

针对7B04铝合金开展了变形温度为470~530℃,应变速率为0.0003~0.01s~(-1)的高温超塑性拉伸实验,研究了材料的超塑性变形行为和变形机制。结果表明,7B04铝合金的流动应力随着变形温度的升高和应变速率的降低而逐渐减小,伸长率随之增加;在变形温度为530℃,应变速率为0.0003s~(-1)时,7B04铝合金的伸长率达到最大1105%,超塑性能最佳;应变速率敏感性指数m值均大于0.3,且随变形温度的升高而增加;在500~530℃的变形温度范围内,m值大于0.5,表明7B04铝合金超塑性变形以晶界滑动为主要变形机制;变形激活能Q为190kJ/mol,表明7B04铝合金的超塑性变形主要受晶内扩散控制;7B04铝合金超塑性变形中在晶界附近有液相产生,且适量的液相有利于提高材料的超塑性能。     

定向凝固 NiAl/Cr(Mo,Hf)合金的微观组织及力学性能

研究了定向凝固NiAl-28Cr-5.85Mo-0.15Hf合金的微观组织与在293～1373K温度范围内的力学性能.结果表明:合金是由NiAl枝晶轴和枝晶间区(NiAl和Cr(Mo)相的共晶)组成的.经过长期固溶时效处理NiAl/Cr(Mo)合金析出少量弥散分布的Huesler相,其余Hf以固溶体方式存在.DSNiAl-28Cr-5.85Mo-0.15Hf合金具有明显的韧脆转变行为,韧脆转变温度依赖于应变速率.室温拉伸断口呈现明显的解理断裂,而韧脆转变温度在以上时,合金具有较大的变形量,断口上有许多韧窝,呈现明显的塑性断裂特征.     

Mechanisms of cavity growth in a fine-grained 7475 Al superplastic alloy

Under creep conditions, cavity growth may be controlled by vacancy diffusion or power-law creep. The two growth mechanisms are examined with reference to a superplastic 7475 Al alloy as a function of test temperature, superimposed strain rate and starting grain size. It is found that power-law cavity growth by plastic deformation of the matrix surrounding the cavities dominates at all test conditions. In addition, growth and interlinkage of cavities is an important parameter in controlling the ease and type of fracture and is enhanced by the ease of superplastic deformation.     

High Temperature Deformation of a β''''(NiAl) Precipitation Strengthened Ferritic Alloy

A β'(NiAl) precipitation strengthened ferritic Fe-19Cr-2Al-4Ni alloy was tested under low cycle fatigue and creep at elevated temperatures. The dislocation microstructures developed were examined by transmission electron microscopy (TEM). The deformation behavior of the alloy was interpreted in terms of dislocationprecipitate configurations and interactions.fatigue deformation.     

异步轧制AZ31镁合金板材的超塑性工艺及变形机制

经过异步轧制工艺获得AZ31镁合金薄板。在300~450℃范围内,分别通过5×10-3,1×10-3s-1和5×10-4s-1不同应变速率进行高温拉伸实验研究其超塑性变形行为,计算应变速率敏感指数m值、超塑性变形激活能Q及门槛应力σ0值。通过EBSD分析和扫描电镜观察拉伸断裂后的断口形貌,分析AZ31镁合金的超塑性变形机制。结果表明:AZ31镁合金的塑性变形能力随着变形温度的升高及应变速率的降低而增强。当拉伸温度为400℃、m=0.72、应变速率为5×10-4s-1时,AZ31具有良好的超塑性,伸长率最大为206%。温度为400℃时,异步轧制AZ31镁合金的超塑性变形是以晶格扩散控制的晶界滑移和基面滑移共同完成的。     

Effect of alloying element modification on superplastic deformation properties of Ti–4Mo–4Al–2Sn–0·5Si (IMI550)

Abstract

The superplastic deformation properties of a commercial titanium alloy, IMI550 (Ti–4Mo–4Al–2Sn–0·5Si, wt-%) are compared with a specially melted ‘modified’ alloy in which 1 wt-%Mo (slow diffusing element) is replaced with 1 wt-%Fe (fast diffusing element) on the basis that the diffusional properties of the β phase, to which these alloying elements segregate, is a significant factor in determining the overall flow properties. It is shown that the superplastic deformation properties of both alloys in the temperature range 800–850°C develop with strain as the initial heterogeneous α + β structure develops into uniform duplex equiaxed microstructures. Thereafter, the modified alloy exhibits enhanced superplastic properties (reduced flow stresses in the strain rate range 5 × 10^-5–5 × 10^-3 s^-1). The results are analysed quantitatively on the basis of the Ashby and Verrall model applied to the α and β phases combined according to the isostress model for two phase deformation which accounts for the interaction of the α and β phases.     

AZ61镁合金薄板超塑性变形特征的SEM研究

利用扫描电镜(SEM)和超塑性拉伸实验对一次热挤压加工成型的AZ61镁合金薄板(晶粒尺寸～12μm)超塑性变形特征进行了研究.结果显示,在最佳的变形温度(623K)和应变速率(1×10-4s-1)条件下,可获得的最大的超塑性形变量为920%.在523～673 K实验温度和1×10-2～1×10-5s-1应变速率范围内,材料的应变速率敏感指数(m值)随实验温度升高和应变速率的降低而增加.较高的m值(0.42～0.46)对应于晶界滑动机制(GBS),而较低的m值(0.22～0.25)则对应于位错滑移机制.变形温度和应变速率是影响超塑性变形量和变量机制的主要因素.     

Reactive Milling and Mechanical Properties of NiAl Composite with HfC Dispersoids

A NiAl-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni,Al,Hf and C powders.The formation mechanism of NiAl-HfC during milling can be attributed to two chemical reactions:Ni Al→NiAl ΔH;Hf C→HfC ΔH,induced by mechanical collision in a certain period of time,which results in an abrupt exothermic reaction.Hot pressing(HP) and hot isostatic pressing(HIP) have been used to make the NiAl-10HfC compacts near fully dense.Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAl-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAl-10TiB2 composite.In the meantime,yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.     

The study of the technology parameters on the superplasticity of the new Al–Zn–Mg–Cu–Ni–Zr base alloy

Al–Zn–Mg–Cu aluminum alloy contain 0.3% Zr and 4% Ni was processed by traditional hot and cold rolling with a total reduction from 0  to  80%. The relationship between superplastic behavior and reduction of cold deformation and casting cooling rate was analyzed. It is shown that the decrease in the reduction of cold rolling do not significantly influence on flow stress and elongation. Decrease in casting cooling rate leads to insignificantly decrease in superplastic indicators. Alloy exhibits advanced superplasticity: the elongation of 400–800% at the strain rates of (5 × 10^–3–1 × 10^–1) s^–1.     

NiAl合金的超塑性行为及其变形机制

研究了等原子比NiAl合金的NiAl-25Cr,NiAl-20.4Fe-Y,Ce,NiAl-30Fe-Y合金的超塑性行为及其变形机制,结果表明,几种合金在一定条件下均表现出超塑性行为,单相NiAl超塑性变形源于变形过程中所发生的动态回夏及再结晶,两相及多相NiAl合金的超塑性变形机制则是晶粒的转动和界面的滑动。     

The phosphorus effect on the superplastic deformation of NiAl

The P effect on the superplastic deformation of NiAl has been investigated. It is shown that P segregates to grain boundaries and the segregation has profound influence on the high temperature tensile properties of the NiAl alloy. The segregation retards dynamic recovery and recrystallization that leads to a decrease in elongation and enhancement in cavitation compared with the stoichiometric NiAl. Therefore, the P has harmful effect on the superplastic deformation of NiAl.     

Microstructural evolution and superplastic behavior in friction stir processed Mg–Li–Al–Zn alloy

A Mg–Li–Al–Zn alloy was friction stir processed (FSP) under water, and the microstructures and superplastic behavior in the FSP alloy were investigated. The FSP Mg–Li–Al–Zn alloy consisted of a mixed microstructure with fine, equiaxed, and recrystallized α (hcp) and β (bcc) grains surrounded by high-angle grain boundaries, and the average grain size of the α and β grains was ~1.6 and ~6.8 μm, respectively. The fine α grains played a critical role in providing thermal stability for the β grains. The FSP Mg–Li–Al–Zn alloy exhibited low-temperature superplasticity with a ductility of 330 % at 100 °C and high strain rate superplasticity with ductility of ≥400 % at 225–300 °C. Microstructural examination and superplastic data analysis revealed that the dominant deformation mechanism for the FSPed Mg–Li–Al–Zn alloy is grain boundary sliding, which is controlled by the grain boundary diffusion in the β phase.     

SiC晶须增强铝基复合材料超塑性

采用高温拉伸、透射电镜、X射线衍射仪、差示扫描量热计和超塑性经典理论,对低压浸渗、小挤压和热轧制备的SiC晶须增强2024Al基复合材料超塑性的力学行为和变形机制进行了研究。研究表明:复合材料的晶粒细小,尺寸约为1 μm;在温度为788 K、初始应变速率为3.3×10-3s-1的拉伸条件下,超塑伸长率为370％;DSC曲线上有一小的初期熔化吸热峰,其温度相应于偏晶反应:Al+Al₂Cu+Cu₄Mg₅Si₄Al_<em>x→液相+Mg₂Si,785 K;超塑性变形的主导机制为传统的晶界扩散机制和适量液相共同控制的晶界(界面)滑动。     

Creep and microstructure in ultrafine-grained 5083 Al

Creep and microstructure in ultrafine-grained (UFG) 5083 Al were investigated at 473 K. UFG 5083 Al was prepared by consolidating the cryomilled alloy powders via hot isostatic pressing followed by extrusion. The creep microstructure developed in the alloy was examined by means of transmission electron microscopy. The results show that the relationship between stress and strain is sigmoidal. Such a sigmoidal behavior is similar in trend to those reported for solid-solution alloys and superplastic alloys. An analysis of the mechanical data along with the consideration of several microstructural findings related to dislocation activity and configuration indicates that the alloy behaves as a superplastic alloy and not as a solid-solution alloy. Also, it is shown that the superplastic behavior of UFG 5083 Al is characterized by the presence of a threshold stress whose origin is most likely related to an interaction between impurities, which are able to segregate at nanoscale dispersion particles introduced as a result of processing, and dislocations, which are captured at the departure side of the particles.     

TC18钛合金的超塑性行为与变形机制

通过高温拉伸实验研究TC18钛合金在温度为720~950℃,初始应变速率为6.7×10~(-5)~3.3×10~(-1)s~(-1)时的超塑性拉伸行为和变形机制。结果表明:TC18钛合金在最佳超塑性变形条件下(890℃,3.3×10~(-4)s~(-1)),最大伸长率为470%,峰值应力为17.93MPa,晶粒大小均匀。在相变点Tβ(872℃)以下拉伸,伸长率先升高后下降,在温度为830℃,初始应变速率为3.3×10~(-4)s~(-1)时取得极大值373%,峰值应力为31.45MPa。TC18钛合金在两相区的超塑性变形机制为晶粒转动与晶界滑移,变形协调机制为晶内位错滑移与攀移;在单相区的超塑性变形机制为晶内位错运动,变形协调机制为动态回复和动态再结晶。