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2021 ◽  
Vol 1035 ◽  
pp. 108-113
Author(s):  
Lin Xiang ◽  
Bin Tang ◽  
Jian Quan Tao ◽  
Qiang Chen ◽  
Zhi Hui Xing ◽  
...  

The effect of processing parameters on meta-dynamic recrystallization (MDRX) and the microstructural characteristics evolution of TiAl alloy with high Nb containing during annealing period were studied through double-pass hot compression tests. The results indicated that the occurrence of MDRX had a strengthening effect to flow behavior of the present alloy, resulting in grain equalization. And the high temperature and large strain were beneficial for the occurrence of MDRX, resulting in the increase of recrystallization grains. For the present alloy, MDRX rate is low, hence, enough annealing time is needed for MDRX during inter-pass annealing. Besides, dislocation density is consumed with the occurrence of MDRX.


Author(s):  
Mahmoud Al-Elaimi ◽  
Farida Hamioud ◽  
G. I. Ameereh ◽  
A. A. Mubarak

Density functional theory (DFT) within Wien2k code is utilized to compute the mechanical, thermal, electronic, magnetic and thermoelectric properties of the cubic spinel CoV2O4. The ground state lattice constant of CoV2O4 alloy agrees with previous literature. The calculated elastic constants of CoV2O4 predict that the present alloy is anisotropic, elastically stable and brittle. Beneficial acoustical applications are expected for the present alloy due to its high calculated Debye temperature and average sound velocities values. The longitudinal and transverse sound velocities modes of vibrations are found maximum along [110] directions compared to [100] and [111] directions. The calculated DOS and band structure show that CoV2O4 is electronically stable. The present alloy possesses a total magnetic moment of 12.0 [Formula: see text] and is classified as a half-metallic ferromagnet. CoV2O4 shows [Formula: see text]-type behavior and favors holes as charge carriers. The present alloy owns beneficial thermoelectric properties and can be used in thermoelectric applications.


Author(s):  
P. Parameswaran ◽  
A.M. Rameshbabu ◽  
G. Navaneetha Krishnan ◽  
R. Yogeshwaran ◽  
R. Ramkumar

AbstractHere, the corrosion properties of chromium (Cr) added to a copper-aluminum-nickel (Cu-Al-Ni) alloy were studied. Primarily, the alloy samples were prepared by increasing the percentages of Cr composition in the following series of 4%, 8% and 12% by keeping other alloying elements as constants. The alloy was made using the powder metallurgical technique. Consequently, hot forging was done on the sintered specimen. Both hypothetical and authentic densities were found for the hot forged samples which showed that the densities kept on increasing with the addition of Cr. The Cr embellishments were exposed using optical microscopy of varying magnifications. The corrosion properties achieved from the potentiostat showed that the corrosion resistance upsurges more than the other commercially available nickel-aluminum-bronze (NAB) alloys due to the Cr embellishments. The corroded surface was then investigated using scanning electron microscopy (SEM) which disclosed the formation of different κ phases along with an α matrix and other intermetallic phases in the present alloy. Furthermore, hardness tests were taken and these established that the hardness increases with Cr accompaniments. Thus, the present alloy can be endorsed as a novel material (Cu-Al-Ni-Cr) in the propellers of ships in which both hardness and corrosion resistant are obligatory.


2015 ◽  
Vol 29 (10n11) ◽  
pp. 1540009
Author(s):  
Liang Cheng ◽  
Xiangyi Xue ◽  
Bin Tang ◽  
Hongchao Kou ◽  
Jinshan Li

In this paper, ingot breakdown process of a high Nb containing TiAl alloy with a chemical composition of Ti –42.63 Al –8.11 Nb –0.21 W –0.09 Y (at.%) has been investigated under conventional forging conditions. It was found that the present alloy possesses superior hot-workability that can be successfully forged by conventional upsetting route due to the appearance of large amount of β/B2 phase, though shear band was observed in the forged-pancake. Further studies revealed that hot-working performed in (α + β) phase region which can effectively impede the β → α transformation and thus significantly increase the volume fraction of β/B2 phase. In contrast, the amount of β/B2 phase was notably reduced by heat treatment at the same conditions. This stress-induced effect is considered to be responsible to the superior hot-workability of the present alloy and the mechanism has been discussed and reasonably clarified. It was also suggested that the stress-induced effect has practical significance that it allows the implementation of conventional multi-step forging process which can develop fine and uniform microstructures suitable for secondary processing.


2013 ◽  
Vol 750-752 ◽  
pp. 659-662
Author(s):  
Zhong Qiu Cao ◽  
Feng Chun Li ◽  
Ying Shen

The oxidation of a ternary Cu-Ni-Co alloy containing about 20 at.% Ni and 75 at.% Co, balance Cu (Cu-20Ni-75Co), was studied at 600-800°C in 0.1MPa pure O2. The kinetic curves for the present alloy are irregular and deviate from the parabolic rate law and are composed of three quasi-parabolic stages. The oxidation rates decrease continuously with time more rapidly than required by the parabolic rate law. These indicate that the scales become more protective with the increment of time. The oxidation rates of the present alloy increase with the increment of temperature. Cu-20Ni-75Co alloy formed a dark external layer composed of Co3O4 followed by a slightly lighter internal layer of CoO. Obviously, adding 20 at% Ni to Cu-75Co alloy is able to decrease the critical Co content required to form the most stable oxide and finish a transformation from the mix internal oxidation to the formation of the exclusive external scales of Co oxides.


2010 ◽  
Vol 146-147 ◽  
pp. 79-88
Author(s):  
Lian Deng Wang ◽  
Ding Yi Zhu ◽  
Zhe Liang Wei ◽  
Yong Lu Chen ◽  
Li Guang Huang ◽  
...  

The Al-20%Si alloy was prepared by mixing the high temperature melt of hypereutectic Al-30%Si alloy with the pre-crystallized low temperature hypoeutectic Al-10%Si alloy melt and then superheating the mixture, i.e., melts mixing and superheating (for short: MMS), combining with chemical metamorphism. The effect of pre-crystallized characteristic of the mixed melt on microstructure of Al-20%Si alloy was then investigated, The primary Si granules of the sample, poured by melt mixing with different composition and temperature, were well distributed with a grain size of less than 36μm. And after superheating, the primary Si phase of the mixed melt could be further refined and distributed more uniformly, which if adding the modificator into the mixed melt, the size of primary Si were been deceased and refined by less than 20μm. The analysis result shows that the decrease in the temperature of the mixed melt, from the average temperature of 740 °C for the mixture of Al-30%Si (900°C) and Al-10%Si (580°C) to 670°C for present alloy, leads to the increase in the degree of undercooling, and consequently to the refinement of primary Si. During the superheating, the growth, local melting, as well as the proliferation of primary Si occurred because of the unhomogeneous micro-distribution of the temperature and composition within the mixing melt, resulting in the further decrease in the grain size of primary Si. And adding the modificator could promote the effect of modification of primary Si of MMS process on the hypereutectic Al-Si alloy.


2008 ◽  
Vol 569 ◽  
pp. 149-152
Author(s):  
Sun Ki Kim ◽  
Han Sol Kim ◽  
Won Yong Kim

This study is to examine wear properties of Ti-Nb-Si alloys under dry condition and to investigate its wear mechanism. A ball-on-disc type wear testing machine was used to evaluate the wear factor. Optical microstructure observation revealed that the microstructure appeared to mixture appearance consisting of β phase and small amount of α″ martensite phase. Yield strength increased with increasing Nb and Si content. Wear resistance of the present alloy are strongly dependent upon yield strength and elastic modulus. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis confirmed the tribo-chemical reaction between the alumina ball and the present alloy occurs due to decomposition of alumina to aluminum.


2007 ◽  
Vol 546-549 ◽  
pp. 2151-2156 ◽  
Author(s):  
Won Yong Kim

We have newly designed a metastable β Ti-Nb-Si based alloy with biocompatible alloying elements without containing toxic V or Al for orthodontic applications. Microstructures and pseudoelastic behavior of β Ti-Nb-Si alloys were investigated in order to correlate the pseudoelasticity and microstructure together with martensite transformation. Nb and Si alloying to the present alloy make β phase to be stable. It is found that metastable β phase is favorable to display pseudoelastic behavior than stable or unstable β phase. Optical microscope (OM) revealed that stress-induced martensitic transformation takes place during room temperature deformation in the present alloys. Within the alloys having β (bcc) phase studied the alloy with low content of Si appeared to exhibit a dominant behavior for stress-induced martensitic transformation than that with high content of Si. After recrystallization heat treatment pseudoelasticity of the present alloy appeared to be prominent. The pseudoelastic behavior of this alloy was correlated to the stress-induced martensite transformation. Pseudoelasticity of the present alloys is hindered by the development of {001}<110> rotated cube component.


2007 ◽  
Vol 22 (4) ◽  
pp. 1093-1097 ◽  
Author(s):  
J.B. Qiang ◽  
W. Zhang ◽  
G.Q. Xie ◽  
A. Inoue

The addition of Ti, Nb, or Ta altered the crystallization behavior of the Zr65Al7.5Cu27.5 glass, and a metastable nanoscaled I-phase was obtained on primary crystallization of these quaternary glasses. The complete substitution of Al by Nb also led to the precipitation of I-phase upon crystallization. Negative heats of mixing between the addition metals and the transition metals of the mother alloy were demonstrated to be not a necessary condition for I-phase formation in the present alloy system.


2007 ◽  
Vol 539-543 ◽  
pp. 647-652 ◽  
Author(s):  
Han Sol Kim ◽  
Won Yong Kim

Microstructures and mechanical properties including elastic modulus were investigated in terms of ternary alloying elements Si addition, Nb content variations and tensile test. Martensite structure with α'(hcp) or α"(orthorhombic) was observed in Ti-xNb-1.5at.%Si, where x=10-20at.%. The crystal structure of martensite formed from water quenching process was largely dependent upon Nb content but does not on Si content. On the basis of experimental results obtained, it is suggested that Si has an effective role to suppress the precipitation of ω phase leading to reduction in elastic modulus in the metastable β phase region. Metastable β phase region was superior to reduce the elastic modulus than stable β phase region in the present alloy system. The minimum value of elastic modulus was measured to 48GPa. We have found that stress-induced martensitic transformation takes place during the deformation in the present alloys. Within the alloys having β(bcc) phase studied Nb-poor region appeared to exhibit a dominant behavior for stress-induced martensitic transformation than Nb-rich region. This result suggests that metastable β phase is superior to stable β phase for the occurrence of stress-induced martensitic transformation in the present alloy system.


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