scholarly journals Evolution of Microstructure and Microsegregation of Ti-45Al-8Nb Alloy during Directional Solidification

2018 ◽  
Vol 2018 ◽  
pp. 1-9
Author(s):  
Xiangjun Xu ◽  
Rui Hu ◽  
Junpin Lin ◽  
Jian Guo
Keyword(s):  
Mushy Zone ◽  
Solidification Rate ◽  
Solidus Temperature ◽  
Melting Zone ◽  
Optical Microscope ◽  
Directionally Solidified ◽  
Good Oxidation Resistance ◽  
Columnar Grains ◽  
Columnar Grain ◽  
Evolution Of Microstructure

High Nb-containing TiAl alloys have good oxidation resistance and mechanical properties, but the microstructure and the properties are substantially affected by the segregation. To quantitatively investigate the segregation behavior of Al during solidification, microstructures of directionally solidified (DS) Ti-45Al-8Nb (in atomic percent) alloy prepared at withdrawing rates of 30 μm/s and 200 μm/s and a temperature gradient of 4200 K/m were observed by optical microscope and electronic probe microanalyzer. The microsegregations were characterized by wave dispersive spectroscopy. The results show that the DS ingots include the no melting zone, directionally solidified zone with columnar grains, mushy zone, and quenched liquid zone. The primary dendritic arm spacings are 353 μm and 144 μm, respectively, for the two ingots. But the solidified microstructures of the ingots are large lamellar colonies, which contain a few B2 patches and γ bands induced by microsegregation. From dendritic zone to columnar zone, the volume fractions of B2 patches and γ bands decrease. The segregation extents of Al and Nb decrease with the increase of solidification rate. There exists an obvious back diffusion process of Al during solidification and cooling after solidification. According to evolution of Al concentration profiles from mushy zone to columnar grain zone, interdiffusion coefficient for Al in β-Ti at near solidus temperature is semiquantitatively calculated, and the value is (6 – 11) × 10−11 m2/s.

Comparison of Solidification Behavior Between Underwater Wet Welding and Dry Welding

2011 ◽  
Author(s):  
Faisal M. Al-Abbas ◽  
Tariq A. Al-Ghamdi ◽  
Stephen Liu
Keyword(s):  
Solidification Rate ◽  
Welding Current ◽  
Grain Morphology ◽  
Travel Speed ◽  
Welding Parameters ◽  
Data Set ◽  
Columnar Grains ◽  
Columnar Grain ◽  
Grain Width ◽  
Solidification Substructure

The solidification substructure, both mode and size, has influence on the mechanical properties of weld joints. Controlling the solidification substructure by obtaining finer grains will generally result in enhancement of the weld joint quality and properties. Thus, it is essential to understand how welding parameters including voltage, current and weld travel speed as well as the welding environment (air and water) affect the solidification substructure. This work presents the effects of welding parameters on columnar grain morphology for both wet and dry welds. Also it compares the solidification rate and columnar grain size (width and length) between the dry welds and wet welds. For fair comparison, the welding parameters of both dry welds and wet welds were maintained similar. The solidification rate of wet welds is faster than that for the dry welds. A maximum difference of 22% was observed at half distance from the fusion line to the weld centerline. For wet welds, the observations revealed that the average columnar grain width and length of wet welds decrease with increasing electrode angle and decreasing welding travel speed. On the other hand, the columnar grain width decreased with increasing welding current. Also, as the welding current increased the average columnar grain length increases. Dry welds differed from wet welds in that the columnar grain average length decreased as the welding current increases. Moreover, the wet weld columnar grains are finer than those found in the dry welds at low welding current, namely 110A and 120A, whereas the wet weld columnar grains are comparable or coarser at high welding current, e.g.130 A and 140A. Statistical analysis of the columnar grain aspect ratio data set using Student’s-t test resulted in low t-value, 0.329 for low current welds, while high t-value, 7.775, was obtained for the welds made at high welding current. Results revealed that the columnar grain morphology in wet welds and dry welds are statistically different at low welding current 110A while columnar grains in dry and wet welds are similar at high welding current 140A.

Magnetic and Mechanical Properties of Directionally Solidified Fe-6.5wt.%Si Alloy

2011 ◽  
Vol 687 ◽  
pp. 122-128
Author(s):  
Y. S. Deng ◽  
Xian Shi Fang ◽  
Feng Ye ◽  
Y. Qiao ◽  
Jun Pin Lin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Directional Solidification ◽  
Grain Growth ◽  
Magnetic Induction ◽  
Crystal Orientation ◽  
Grain Structure ◽  
Directionally Solidified ◽  
Columnar Grains ◽  
Columnar Grain ◽  
Saturation Magnetic Induction

Directional solidification technique was employed to produce Fe-6.5wt.%Si alloy with coarse columnar-grain structure, which was almost single crystal. The sectional diameters of columnar grains range from 2.2 to 6.8 mm. The saturation magnetic induction was 2.39 T. In this work, grain growth started from either a Fe-6.5wt.%Si crystal which was not melted at bottom of the specimen or a freely nucleated Fe-6.5wt.%Si crystal as the specimen was completely melted. It was found that the starting situation of the directional solidification plays an important role in the crystal orientation, and hence in properties.

Continuous Cooling Transformation of Overcooling Austenite and Structure Evolution of Si Steel

2013 ◽  
Vol 652-654 ◽  
pp. 947-951
Author(s):  
Hui Li ◽  
Yun Li Feng ◽  
Da Qiang Cang ◽  
Meng Song
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
Optical Microscope ◽  
Structure Evolution ◽  
Upward Trend ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Hardness Tester ◽  
Gleeble 3500 ◽  
Evolution Of Microstructure

The static continuous cooling transformation (CCT)curves of 3.15 Si-0.036 C-0.21 Mn-0.008 S-0.008 N-0.022 Al are measured on Gleeble-3500 thermal mechanical simulator, the evolution of microstructure and the tendency of hardness are investigated by optical microscope (OM) and hardness tester. The results show that there is no evident change in microstructure which mainly are ferrite and little pearlite under different cooling rates, but the transition temperature of ferrite is gradually reduced with the increase of cooling rate. When the cooling rate is increased from 0.5°C/s to 20°C/s, the ending temperatures of phase transformation are decreased by 118°C, when cooling rate reaches to 10, Widmanstatten ferrite appears. The hardness of the steel turns out gradual upward trend with the increase of cooling rate.

Evolutions of Microstructure for Multilayered Al-Mg Alloy Composites by Accumulation Roll Bonding (ARB) Process

2011 ◽  
Vol 411 ◽  
pp. 527-531
Author(s):  
Bing Zhang ◽  
Zhong Wei Chen ◽  
Shou Qian Yuan ◽  
Tian Li Zhao
Keyword(s):  
Multilayer Structure ◽  
Optical Microscope ◽  
Alloy Layer ◽  
Mg Alloy ◽  
Micro Hardness ◽  
Roll Bonding ◽  
Fine Grained ◽  
Hardness Tester ◽  
Average Grain Size ◽  
Evolution Of Microstructure

In this paper, accumulative roll bonding (ARB) has been used to prepare the Al/Mg alloy multilayer structure composite materials with 1060Al sheet and MB2 sheet. The evolution of microstructure of the cladding materials during ARB processes was observed by optical microscope, scanning electron microscopy, and micro-hardness was measured by micro-hardness tester. The results show that a multilayer structure material of Al/Mg alloy with excellent bonding characteristics and fine grained microstructure was prepared by ARB processes. With the ARB cycles increasing, Mg alloy layer in multilayer composite material was necked and fractured, and the hardness of the Al and Mg alloy was increased. Average grain size was less than 1μm after ARB4 cycles.

The Mechanical and Deformation Behavior of TWIP Steel Prepared by Directional Solidification

2014 ◽  
Vol 783-786 ◽  
pp. 761-765 ◽  
Author(s):  
Dan Wang ◽  
Kun Wang ◽  
Zi Mu Shi ◽  
Fu Sheng Han
Keyword(s):  
Mechanical Properties ◽  
Strain Hardening ◽  
Twip Steel ◽  
True Strain ◽  
Longitudinal Direction ◽  
True Stress ◽  
Grain Structure ◽  
Directionally Solidified ◽  
Twip Steels ◽  
Columnar Grain

A directionally solidified TWIP steel (Fe-25Mn-2.5Al-2.5Si) was prepared by liquid metal cooling technology. The microstructure and mechanical behavior were examined and compared with usually solidified samples. The directionally solidified TWIP steel shows a typical columnar grain structure, and the maximum true stress and true strain along the longitudinal direction of the sample are 1060MPa and 71% respectively. As a comparison, the usually solidified samples shows an equiaxed grain microstructure with the maximum true stress and true strain of only 994MPa and 58%, respectively. Moreover, the two solidification modes also lead to very different strain hardening behavior, particularly in the changes of strain hardening rate with strain. This suggests that the grain boundary plays a key role in the mechanical properties of TWIP steels, and changing the grain boundaries can be effective to improve the comprehensive mechanical properties of TWIP steels.

Effect of Shot Peening on Microstructure and Properties of 34CrMo4 Alloy

2018 ◽  
Vol 934 ◽  
pp. 105-110 ◽  
Author(s):  
Ke Jian Li ◽  
Qiang Zheng ◽  
Yue Lin Qin ◽  
Xiao Wei Liu
Keyword(s):  
Plastic Deformation ◽  
Corrosion Resistance ◽  
Shot Peening ◽  
Electrochemical Impedance ◽  
Corrosion Current ◽  
Optical Microscope ◽  
Microstructure And Properties ◽  
Before And After ◽  
Sever Plastic Deformation ◽  
Evolution Of Microstructure

Plastic deformation can induce surface modification, such as shot peening (SP) on workpiece surface is the hot issue of recent scientific research. SP is the efficient way to improve mechanical behavior of specimens by inducing sever plastic deformation on their surface. Nevertheless, this surface treatment induced complex microstructural evolutions such as grain refinement, will enhance the corrosion resistance of specimens. In this work, the microstructure and properties of 34CrMo4 alloy of before and after SP for 20 min have been investigated. The evolution of microstructure and properties were analyzed from the surface and cross-section. The microstructure morphology at the different depth was determined by optical microscope. The results show grain size is increasing with the depth, and the microhardness and compressive residual stress decrease gradually. In terms of corrosion resistance, the 50 μm depth specimen has the best property than other depth, which the potential and corrosion current density are-0.484 V and-5.72 Acm-2, respectively. The maximum polarization resistance is 2055 Ωcm2by capacitive arc radius of electrochemical impedance spectroscopy.

Resonant Response and Random Response Analysis of Mistuned Bladed Disk Consisting of Directionally Solidified Blade

2015 ◽  
Author(s):  
Yasutomo Kaneko ◽  
Kazushi Mori ◽  
Hiroharu Ooyama
Keyword(s):  
Elastic Constants ◽  
Rupture Strength ◽  
Turbine Blades ◽  
Response Analysis ◽  
Resonant Response ◽  
Random Response ◽  
Directionally Solidified ◽  
Columnar Crystal ◽  
Bladed Disk ◽  
Columnar Grains

Recently, DS (Directionally Solidified) and SC (Single Crystal) alloys have been widely applied for gas turbine blades instead of CC (Conventional Casting) alloys, in order to improve the creep rupture strength. The DS blade consists of several columnar grains of SC, where the growing direction of the columnar crystal is set to the direction of the centrifugal force. Because the elastic constants of the DS blade are anisotropic, the mistuning characteristics of the bladed disk consisting of the DS blades seem to be different from those of the CC blade. In this study, the resonant response and random response analysis of mistuned bladed disks consisting of the DS blades are carried out, considering the deviations of the elastic constants and the crystal angle of the DS blade. The FMM (Fundamental Mistuning Model) and the conventional modal analysis method are used to analyze the vibration response of the mistuned bladed disk. The maximum resonant response and random response of the mistuned bladed disk consisting of the DS blades are estimated by the Monte Carlo simulation combining with the response surface method. These calculated results for the DS blades are compared with those of the CC blades. From these results, it is concluded that the maximum response of the mistuned bladed disk consisting of the DS blades is the nearly same as that of the CC blades. However, in the design of the tuned blade, where the blade resonance should be avoided, it is necessary to consider that the range of the resonant frequency of the DS blade becomes wider than that of the CC blade.

Relationship between η phase formation and solidification rate in directionally solidified IN792 + Hf alloy

1999 ◽  
Vol 15 (11) ◽  
pp. 1221-1224 ◽  
Author(s):  
W.R. Sun ◽  
J.H. Lee ◽  
S.M. Seo ◽  
S.J. Choe ◽  
Z.Q. Hu
Keyword(s):  
Phase Formation ◽  
Solidification Rate ◽  
Directionally Solidified

Evolution of microstructure and microsegregation in Ni-Mn-Ga alloys directionally solidified under axial magnetic field

2018 ◽  
Vol 758 ◽  
pp. 54-61 ◽  
Author(s):  
Long Hou ◽  
Yanchao Dai ◽  
Yves Fautrelle ◽  
Zongbin Li ◽  
Zhongming Ren ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Axial Magnetic Field ◽  
Directionally Solidified ◽  
Evolution Of Microstructure
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