Effect of Homogenization Time and Cooling Rate on Martensitic Transformations in Ti-57.5%wtNi Alloy

2010 ◽  
Vol 297-301 ◽  
pp. 339-343
Author(s):  
P. Movahed ◽  
Ali Shokuhfar ◽  
H. Kaffash ◽  
A. Etaati ◽  
H. Bolvardi ◽  
...  

NiTi alloys containing more than 55%wt nickel undergo precipitation of Ni4Ti3, Ni3Ti2, and Ni3Ti phases during various heat treatments which could have a great effect on the chemical composition of the matrix and behavior of alloy. In this investigation, a NiTi alloy with Ti-57.5%wt nickel content, produced by vacuum induction melting in a graphite crucible, were subjected to the homogenization heat treatments in 1100oC and for various time periods (0.5, 1, 2, and 4 hours). The subsequent cooling was conducted in different cooling media (furnace and air) in order to examine the effect of cooling rate. Microstructural investigations show Ni4Ti3 particles with bimodal size distribution in furnace cooling. Differential scanning calorimetry demonstrates the correlation between homogenization time and transformation temperatures of the alloy.

2015 ◽  
Vol 1765 ◽  
pp. 121-126 ◽  
Author(s):  
Jackson de Brito Simões ◽  
Francisco Fernando Roberto Pereira ◽  
Jorge Otubo ◽  
Carlos José de Araújo

ABSTRACTShape memory alloys (SMA) are metallic attractive engineering materials due to their capacity to store pre-defined shapes through a thermally induced phase transition from a solid state. This paper aims to evaluate the influence of solubilization thermal treatments on a NiTi shape memory alloy originally fabricated by vacuum induction melting and then reprocessed by plasma melting followed by injection molding (Plasma Skull Push Pull process) into different metal molds (steel, aluminum, brass and copper) in order to compare the thermal properties regarding to its raw state. The thermal treatments of solubilization were carried out at 850°C in different times (2n function, n = 0, 1, 2 and 3, in hours). The influence of solubilizing treatments in the NiTi shape memory alloy was analyzed using the following characterization techniques: Differential Scanning Calorimetry (DSC) and Electrical Resistance as a function of Temperature (ERT). The results demonstrate that the solubilization heat treatments applied on the reprocessed NiTi shape memory alloy through the plasma skull push pull process, provides important changes in the phase transformation of the material. Therefore, it was demonstrated that it is necessary to solubilize the material after melting or remelting the NiTi shape memory alloy via this process to obtain mini-actuators products with homogeneous properties.


2007 ◽  
Vol 465 (1-2) ◽  
pp. 44-48 ◽  
Author(s):  
Niraj Nayan ◽  
Govind ◽  
C.N. Saikrishna ◽  
K. Venkata Ramaiah ◽  
S.K. Bhaumik ◽  
...  

2011 ◽  
Vol 694 ◽  
pp. 704-707
Author(s):  
Z.M. Zhou ◽  
W.J. Huang ◽  
J. Luo ◽  
X.P. Li ◽  
T. Zhou ◽  
...  

The effect of cooling rate on the microstructure of Cu80Cr20 alloys was studied by using vacuum non-consumable arc melting, vacuum induction melting, electromagnetic levitation and splat quenching. The microstructure evolution of the Cr-rich were analyzed by scanning electron microscopy (SEM) and optical microscopy. The results showed that nonuniform Cr-rich dendrite distributes on Cu-rich matrix for arc melted alloys and uniform Cr-rich dendrite distributes on Cu-rich matrix for electromagnetic levitation melted alloys and vacuum induction melted alloys. However, the Cr-rich phase show both dendrites and spheroids for splat quenched alloys. This means liquid phase separation occurred during rapid solidification.


2014 ◽  
Vol 1611 ◽  
pp. 31-36 ◽  
Author(s):  
Jackson de Brito Simões ◽  
Francisco Fernando Roberto Pereira ◽  
Jorge Otubo ◽  
Carlos José de Araújo

ABSTRACTShape Memory Alloys (SMA) metallic materials that change their mechanical and physical properties with temperature variation and mechanical loading, surprising engineers and researchers. In this way, one can develop thermomechanical actuators capable, for example, of generating force by blocking the shape recovery or change the natural frequency of a mechanical system by blocking resonance. The processing of these SMA are countless, each one with its specific limitation and particularity. This study aims to evaluate the influence of rapid solidification of a Ni-Ti SMA that is originally manufactured by Vacuum Induction Melting (VIM) and reprocessed by Plasma Melting (PM) followed by injection molding into different metal molds (steel, brass, aluminum and copper). The influence of such a processing is analyzed through Differential Scanning Calorimetry (DSC) and Electrical Resistance as a function of Temperature (ERT) to determine the effects on transformation temperatures. The results demonstrate that by using the copper mold one can provide greater uniformity of the material properties. Thus, there is the possibility of obtaining different kinds of SMA mini-actuators by PM injection in a copper mold and that includes different shapes and sizes that can be studied further.


2020 ◽  
Vol 17 (3(Suppl.)) ◽  
pp. 0961
Author(s):  
Ali Abadi Aljubouri ◽  
Safa hasan Mohammed ◽  
Mudhafar ali Mohammed

Sn effect on the phase transformation behavior, microstructure, and micro hardness of equiatomic Ni-Ti shape memory alloy was studied. NiTi and NiTiSn alloys were produced using vacuum induction melting process with alloys composition (50% at. Ni, 50% at.Ti) and (Ni 48% at., Ti 50% at., Sn 2% at.). The characteristics of both alloys were investigated by utilizing Differential Scanning Calorimetry, X- ray Diffraction Analysis, Scanning Electron Microscope, optical microscope and vicker's micro hardness test. The results showed that adding Sn element leads to decrease the phase transformation temperatures evidently. Both alloy samples contain NiTi matrix phase and Ti2Ni secondary phase, but the Ti2Ni phase content decreases with Sn addition and this is one of the reasons that leads to decrease the micro hardness of alloy with adding Sn element in a noticeable manner. The micro hardness decreases from 238.74 for NiTi equiatomic alloy to 202 for NiTiSn alloy after heat treatment.


2019 ◽  
Vol 49 (1) ◽  
pp. 71-75
Author(s):  
L. A. SANTOS ◽  
J. OTUBO ◽  
D.A. P. REIS

In this work, samples of the alloy (composed of 50.9% at Ni) were machined and solubilized so all had the same condition for the hot tensile test between the temperatures 350-650 °C. The results showed that yield stress was between 800 and 597.1 MPa and area reduction between 17 and 75% during the hot tensile test in the respective temperatures. The test at 350 °C shows a fragile fracture characteristic verified by the presence of “river marks”, which are characteristic of this type of fracture, because this condition does not promote much plastic deformation. At the other temperatures ductile fracture was observed, with “dimples” that also characterize this type of fracture. This work shows the temperature relationship in the mechanical properties, more specifically the hot tensile test, in NiTi alloy.


2010 ◽  
Vol 643 ◽  
pp. 55-59 ◽  
Author(s):  
Jorge Otubo ◽  
André da Silva Antunes

Earlier works showed that NiTi shape memory alloy production by electron beam melting (EBM) is a viable process in which its main characteristic is the low contamination by impurities such as carbon and oxygen. Some difficulties arise when compared to conventional vacuum induction melting (VIM) process such as composition control and complex machine operation. This work focus on the production of ever made large scale 150mm in diameter NiTi ingot produced by EBM showing its viability. The carbon contamination was only 0.016wt% compared to usual 0.05wt% of VIM process. The ingot radial composition homogeneity was proved by small variation presented by direct and reverse peak martensitic transformations temperatures which was around 2°C.


2007 ◽  
Vol 124-126 ◽  
pp. 1649-1652 ◽  
Author(s):  
Jung Min Nam ◽  
Jae Hwa Lee ◽  
Yun Jung Lee ◽  
Tae Hyun Nam

Ti-51Ni(at%) and Ti-40Ni-10Cu(at%) alloy wires with diameters of 0.3mm, 0.5mm and 0.7mm were prepared by drawing the alloy ingots fabricated by vacuum induction melting. Heating rates of the wires were investigated by measuring changes in temperatures of them while applying currents in the range of 1 A and 6 A to them and cooling rates were investigated by measuring changes in temperatures of them after cutting currents. Heating rate increased with increasing the amount of current, while cooling rate was kept constant. Both heating rate and cooling rate increased with decreasing diameter of wire. This suggested that high amount of current and small wire diameter were required for high heating and cooling rate. Comparing Ti-50Ni alloy wires with Ti-40Ni-10Cu alloy wires, heating rates of the latter was faster than that of the former, although cooling rates were almost same. This suggested that Ti-40Ni-10Cu alloy wires is better than Ti-50Ni alloy wires for the applications requiring high actuating rates.


Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4118 ◽  
Author(s):  
Shifeng Liu ◽  
Song Han ◽  
Liqiang Wang ◽  
Jingbo Liu ◽  
Huiping Tang

The addition of Nb can form a eutectic phase with a NiTi matrix in a NiTi-based shape memory alloy, improving the transition hysteresis of the NiTi alloy. A Ni44Ti44Nb12 ingot was prepared using the vacuum induction melting technique. Under compression deformation, the yield strength of the NiTi–Nb alloy is about 1000 MPa, the maximum compressive strength and strain can reach 3155 MPa and 43%, respectively. Ni44Ti44Nb12 exhibited a superelastic recovery similar to that of the as-cast NiTi50. Meanwhile, the loading–unloading cycle compression shows that the superelastic recovery strain reached a maximum value (2.32%) when the total strain was about 15%, and the superelasticity tends to rise first and then decrease as the strain increases.


2016 ◽  
Vol 863 ◽  
pp. 139-143
Author(s):  
Yu Yang Bian ◽  
Shu Qiang Guo ◽  
Kai Tang ◽  
Wei Zhong Ding

VIM-HMS method is a novel process to extract REEs (rare earth elements) from NdFeB based permanent magnets. The NdFeB materials were melted in graphite crucible by VIM (vacuum induction melting) process, and the carbon saturated NdFeBCsat alloy was obtained. The NdFeBCsat alloy was mechanically pulverized and hydrolyzed in deionized water. In the HMS (Hydrolysis and magnetic separation) process, the neodymium carbide phase in the alloy reacted with water easily, and the rare earth hydroxides and the iron residues were separated by magnetic separation. The purity of the rare earth hydroxides was more than 99%, and the extraction ratio of the REEs is about 93%.


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