(α+β)Dual Phase CuZnAl Shape Memory Alloy

The effect of α phase on CuZnAl shape memo-ry alloy(SMA)has been systematically studied byelectrical resistance method,quantitative measure-ment of micrography and transmission electronmicroscopy(TEM).It is found that,by controllingthe amount of α phase in(α+β)-CuZnAl alloy,phase transformation temperatures can be adjustedprecisely in a wide range,while the good shapememory effect of CuZnAl is kept.In a word,quenching from(α+β)dual phase region is a rea-sonable method of adjusting phase transformationtemperatures for CuZnAl alloy.     

Influence of Moderate Temperature Treatment on Thermal Cycling Behaviour and Mechanical Properties of the CuAINiMnTi Alloys

The influence of moderate temperature treatment after quenching on thermal cycling behaviour andmechanical properties of the CuAlNiMnTi shape memory alloys have been investigated.It is shownthat there will be α phase precipitation in the alloy when it is subjected to quenching followed bymoderate temperature treatment at 600℃.The precipitation of α phase can suppress NiAl-basephase precipitation during subsequent thermal cycling,therefore the stabilization of transformationtemperature during thermal cycling can be achieved.The suitable amount of α phase precipitationcontributes to the improvement of mechanical properties of the alloy by changing the fracturemorphology.     

Abstractsof Selected Articles on metals Published in China

90A0026 Influence of Deformation at MartensiticState on Shape Recovery in Co-Zn-Al Memory Al-loys An investigation of the influence ofdeformation on shape recovery has been put for-ward in Cu-Zn-Al shape memory alloys.Startingat the model of the re-orientation of martensiticvariants,the principle and essentiality of the influ-ence of the amount of pre-deformations on shaperecovery rate η is elucidated.LI Bing,JIANGBohong and XU Zuyao: Acta Metall.Sin.,1989,25(4),A235-A243.     

Effect of Training on Two-way Shape Memory Effect and Its Stability in a Ti-Ni-Hf High Temperature Shape Memory Alloy

The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36Ni49Hfl5 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.     

Effect of Li and Ti Additions on L■α(Al)+Mg_2Si Pseudobinary Eutectic Reaction

Effect of Li and Ti additions on Lα(AI)+Mg2Si pseudobinary eutectic reaction in ternary Al-Mg-Si system has been investigated by thermoanalysis, directional solidification and metallographic techniques in this study. It has been found that Li addition causes decreasing of the volume fraction of Mg2Si, while a little amount of Ti causes to increasing, which is of a great importance to the adjustment of phase constitution and alloy properties. Doping components have little influence on the eutectic temperature.     

ω-Assisted refinement of α phase and its effect on the tensile properties of a near β titanium alloy

In this work, the phase transformation sequence during the continuous heating process(3℃/min) was investigated in a near β titanium alloy. The results show that the staring formation of ω phase is about267℃, and the ending precipitation temperature about 386℃ during the heating process. When the heating temperature is greater than 485℃, there are no ω phase detected within the β matrix. Combined with the microstructural characterization, it is found that ω phase facilitates the nucleation of αphase nearby the ω/β interface and has a great effect on the refinement for α phase. As compared with the specimens directly aged, the specimens with ω-assisted refinement of α phase possess high tensile strength, but there is no yield stage detected on their stress-strain curve. Combined with the analyses of the fracture morphology, the specimens with ω-assisted refinement of α phase present a brittle fracture.This is mainly ascribed to its relatively lager width of grain boundaries and the absence of widmanst?ttenα precipitates.     

Distinct dendritic α phase emerging on the surface of primary α phase in a compressed near-α titanium alloy

The characteristic of the surface morphology of primary α phase was studied in a deformed near-α titanium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α + β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epitaxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.     

Effect of Phosphorus on Stress Rupture Properties of GH4133 Ni—Base Superalloy

The effect of phosphorus on the stress rupture property of GH4133 alloy has been investigated and is compared with that of IN718 alloy. The GH4133 alloy is crept by dislocation movement. Phosphorus has a tendency to prolong the rupture life of some wrought superalloys by inhibiting the dislocation movement. If the phosphorus addition is too high, its effect on impairing the grain boundary cohesion overwhelms that on inhibiting the dislocation movement,and the life of the GH4133 alloy can be shortened. The two functions of inhibiting the dislocation movement and impairing the grain boundary cohesion determine that the optimum phosphorus content in the GH4133 alloy is around 0.011 wt pct. Phosphorus exhibits a greater effect on prolonging the rupture life of IN718 alloy than that of GH4133 alloy. The two alloys are crept by different mechanisms. The intergranular phosphorus-bearing phase is precipitated in the IN718 alloy, while not in the GH4133 alloy. The precipitation of the phosphorus bearing phase can balance the phosphorus segregation at the grain boundaries and allows a more remarkable effect of phosphorus on extending the rupture life of IN718 alloy.     

Effect of Brownian Coagulation on the Liquid-liquid Decomposition in Gas-atomized Alloy Drops

Modeling and simulation have been carried out for Al-Pb alloys to investigate the Brownian coagulation effect on the microstructure development in a gas-atomized drop during the liquid-liquid decomposition. The results indicate that Brownian coagulation has a weak effect on the nucleation and a relatively strong effect on coarsening the minority phase droplets. The influence of Brownian coagulation on the liquid-liquid decomposition decreases with the increase in the diameter （or the decrease in the cooling rate） of the atomized drop.     

Influence of Liquid Structure on Solid Transformation of CuAINi Shape Memory Alloy

Molten Cu-13AI and Cu-13AI-4Ni (mass fraction) alloys have been investigated using X-ray diffraction method. A distinct pre-peak has been found in the structure factors. The pre-peak increases its intensity with decreasing temperature and addition of Ni. The structural unit size corresponding to the pre-peak equals to magnitude of (111) planar distance of phase. The appearance of a pre-peak is due to existence of clusters with -phase-like structure in melt. Quantity and size of clusters increase with decreasing temperature but their structural unit size remains constant. Cu-13AI-4Ni shape memory alloy ribbons can be fabricated by rapid solidification technique. Order degree of martensite and temperature of the reverse martensitic transformation increase with decreasing liquid quenching temperature. phase particles develop from incorporating and growing of the clusters during solidification, thus result in the correlation between liquid structure and solid transformation.     

Influence of α/β interface phase on the tensile properties of laser cladding deposited Ti–6Al–4V titanium alloy

Laser cladding deposited Ti–6Al–4V titanium alloy universally shows more complex microstructures,each of which has significant effect on mechanical properties. Of particular α/β interface phase has been observed in this paper under certain conditions. It demonstrates that the influence of the α/β interface phase on the tensile properties is closely associated with dislocations and twin substructure through comparison experiments. The results show that the α/β interface phase hinders dislocation motion and decreases effective slip length. In addition, the twin substructure has been activated in the α/β interface phase during tensile process and has acted somehow like grain boundaries. Therefore, the strength and the work-hardening rate of the laser cladding deposited Ti–6Al–4V titanium alloy have been significantly improved due to the dynamic Hall–Petch effect. Besides, the α/β interface phase leads to more uniform dislocations distribution, which implies that relative lower local concentrated stress will be produced along the α/β interface phase or colony boundary after the same amount of plastic deformation. Moreover,the twinning-induced plasticity effects in the α/β interface phase further increase the plastic deformation capacity. These results in higher elongation for the laser cladding deposited Ti–6Al–4V titanium alloy.It can be concluded that the current work suggests an effective method to simultaneously improve the strength and plasticity of laser cladding deposited Ti–6Al–4V titanium alloy based on the α/β interface phase.     

A Mathematical Model for Forecasting Distortion of Workpieces with Phase Transformation on Cooling Process

A temperature phase transformation stress coupled 3D nonlinear mathematical model has been proposed for forecast-ing distortion of workpieces on the cooling processes in this paper. Moreover, a series of subroutines were developed on the MARC (analysis research corporation) software platform and the simulation result is basically identical with the experimental one that measured on the workpiece shape with LEITZ equipment. This verifies that the mathematical model and method are feasible.     

Influence of Liquid Structure on Solid Transformation of CuA1Ni Shape Memory Alloy

Molten Cu-13Al and Cu-13AI-4Ni (mass fraction) alloys have been investigated using X-ray diffraction method. A distinct pre-peak has been found in the structure factors. The pre-peak increases its intensity with decreasing temperature and addition of Ni. The structural unit size corresponding to the pre-peak equals to magnitude of (111) planar distance of β phase. The appearance of a pre-peak is due to existence of clusters with β-phase-like structure in melt. Quantity and size of clusters increase with decreasing temperature but their structural unit size remains constant. Cu-13AI-4Ni shape memory alloy ribbons can be fabricated by rapid solidification technique. Order degree of martensite and temperature of the reverse martensitic transformation increase with decreasing liquid quenching temperature.β phase particles develop from incorporating and growing of the clusters during solidification, thus result in the correlation between liquid structure and solid transformation,     

A Mathematical Modei for Forecasting Distortion of Workpieces with Phase Transformation on Cooling Process

A temperature phase transformation stress coupled 3D nonlinear mathematical model has been proposed for forecasting distortion of workpieces on the cooling processes in this paper. Moreover, a series of subroutines were developed on the MARC (analysis research corporation) software platform and the simulation result is basically identical with the experimental one that measured on the workpiece shape with LEITZ equipment. This verifies that the mathematical model and method are feasible.     

Glass ceramics containing ferroelectric phases

Glass ceramics prepared by controlled crystallization of glasses produce fine dispersion of crystallites in a glassy matrix. Glasses containing a mjor portion of constituents of a ferroelectric phase produce crystallites of ferroelectric phase in glass through a suitable heat treatment. The amount of network former in the initial glass has a profound influence on its crystallization behaviour and microstructure of the resulting ferroelectric glass ceramics. The value of dielectric constant and the nature of ferroelectric to paraelectric transition depend on the crystallite size and volume fraction of the ferroelectric phase. These glass ceramics are transparent for crystallite size less than 0·1μm and exhibit large quadratic-electro-optic effect.     

Prediction of Austenitization and Homogenization of Q235 Plain Carbon Steel during Reheating Process

In this paper,the austenitization and homogenization process of Q235 plain carbon steel during reheating is predicted using a two-dimensional model which has been developed for the prediction of diffusive phase transformation(e,g.αto γ).The diffusion equations are solved within each phase(αand γ) and an explicit finite volume technique formulated for a regular hexagonal grid are used.The discrete interface is represented by special volume elements α/γ,an volume element α undergoes a transition to an interface state before it becomes γ.The procedure allows us to handle the displacement of theinterface while respecting the flux condition at the interface.The simulated microstructure shows the dissolution of ferrite particles in the austenite matrix is presented at different stages of the phase transflrmation.Specifically,the influence of the microstructure scale and the hwating rate on the phase transformation kinetics has been investigated.The experimental results agree well with the simulated ones.     

Influence of alloy element partitioning on strength of primary α phase in Ti-6Al-4V alloy

The partitioning effect of Al(α-phase stabilizer) and V elements(β-phase stabilizer) on strength of the primary α phases in the α/β Ti-6 Al-4 V alloy with the bimodal microstructure was investigated.It was found that partitioning of Al and V elements took place in the Ti-6 Al-4 V alloy during the recrystallization process,leading to the variation of the content of Al and V elements in the primary α phases with changing the volume fraction of the primary α phase.Nanoindentation tests reveal a general trend that the strength of the primary α phases increases with decreasing the volume fraction of the primary α phases,and such trend is independent on the loading direction relative to the c-axis of the α phase.The enhanced strength is attributed to the increase of the content of Al element in the primary α phase,but it is not dominated evidently by the change of the V content.The solid solution strengthening contributed from both the elastic strain introduced by the solute atoms and the variation of the density of states was estimated theoretically.     

The Study on Quench Transformation in Ti-10V-2Fe-3Al Alloy

The quench transfomation in a Ti-10V-2Fe-3Alnear B-titanium alloy was studied by meansof X-ray diffraction, transmission electronmicroscopy, and optical micyoscopy. The quenchingtemperatures were above and below the β transustemperature. The phase constitutions of specimensquenched from various solution temperatureswere identified and the phase morphologies wereexamined. In addition, the relationship betweenphase lattice parameters and quenching tempera-tures was given for α, β and α ~(11) phases. Thisalloy has a tendency of precipitation of athermalω phase and formation of stress induced α~(11) mar-tensite from β phase during quenching. Quenchedfrom the temperatures above the β transus tem-perature, the alloy mainly consists of β phase,a small amount of α~(11) martensite and athemalω phase aye also present in the alloy. Afterquenching from the temperatures below the βtransus temperature, the α phase appeaysin the alloy in addition to the phases mentionedabove.     

A Review on the Regulation of Magnetic Transitions and the Related Magnetocaloric Properties in Ni-Mn-Co-Sn Alloys

In Ni-Mn-X(X=In,Sn,Sb) ferromagnetic shape memory alloys,a ferromagnetic transition from paramagnetic to ferromagnetic austenite and a martensitic transformation from ferromagnetic austenite to weak magnetic martensite occur in some particular composition ranges,in which abundant physical properties have been observed by the abrupt change of magnetization and resistivity around their transition temperatures in these alloys.Therefore,tuning the martensitic transformation temperature(TM) and enlarging the workingtemperature interval for Ni-Mn-X(X=In,Sn,Sb) alloys,are of great importance.In the present paper,we will focus on the effect of external factors,including pre-deformation,annealing,and high pressure annealing,on the magnetic transitions and the related magnetocaloric properties in Ni-Mn-Co-Sn ferromagnetic shape memory alloys.Our approaches and the main results in this particular field will be reviewed.     

Effects of Ta Addition on NiTi Shape Memory Alloys

1. IntroductionSince NiTi shape memory alloy have excellentshape memory effect, good mechanical properties, excellent biocompatibility and high corrosion resistance,they have been used for various applications, espysctally in the biomedical fi.ldll~4]. However, the lowX-ray visibility of NiTi shape memory alloys has limited some medical applicatinns. With low X-ray visibility, the detection of the very small implacable devices or tools which are made of NiTi alloys can bevery difficult. So…