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1.
S.?MahantyEmail author Gouthama 《Journal of Materials Engineering and Performance》2016,25(11):4649-4656
In the present research, the Al-Si alloy surface is treated by KrF excimer pulse laser for different number of laser pulses in ambient condition at energy 4.75 J/cm2. The surface microstructural characterization was done by the optical microscope, in situ video recording during laser pulsing, SEM and TEM. The fretting wear test was undertaken to assess the tribological behavior. In situ video recording showed changes in the surface reflectivity with the number of pulses which is related to progressive changes in the surface compositional homogeneity. After ten pulses, signs of rippled structure were observed. The 15 pulse samples showed star-like morphological feature at the central region. The TEM observations showed high density of stacking faults/twins in Si after first pulse treatment. After 15 pulses, nano-crystalline Si precipitates in the size range <5 nm are seen to be homogeneously distributed. A cellular structure with the cell size <100 nm formed in the matrix. These cell boundaries were decorated with the Si nanocrystals. A positive effect in wear resistance property is observed after the 15 pulses treatment. 相似文献
2.
S. Sankaran Gouthama S. Sangal K. A. Padmanabhan 《Metallurgical and Materials Transactions A》2006,37(11):3259-3273
A ferrite-bainite-martensite (F-B-M) microstructure was produced in a medium-carbon microalloyed (MA) steel through two routes,
namely, low-temperature finish forging and rolling, followed by a two-step cooling (TSC) and annealing. Transmission electron
microscopy (TEM) was employed to study the microstructural evolution in control forged and rolled material after TSC followed
by annealing (TSCA). A TEM investigation was also carried out on samples low-cycle fatigue (LCF) tested at low and high total
strain amplitudes of 0.4 and 0.7 pct in case of the forged steel (F-B-M(F)TSCA) and 0.55 and 0.8 pct for the rolled steel
(F-B-M(R)TSCA), respectively. Microstructural changes accompanying the LCF testing were identified. The two-step cooled microstructure
processed through forging (F-B-M(F)TSC) as well as rolling (F-B-M(R)TSC) revealed a complex multiphase microstructure, along
with films and blocks of retained austenite. In both microstructural conditions, vanadium carbide precipitates were too fine
to be identified after the TSC treatment. Annealing after TSC produced a stress-free microstructure. The F-B-M(F)TSCA microstructure
predominantly consisted of granular/lower bainite, lath martensite, and polygonal ferrite with interlath films as well as
blocks of retained austenite, while the F-B-M(R)TSCA microstructure predominantly consisted of lath martensite, granular/lower
bainite, and polygonal ferrite with interlath strips/films of retained austenite. Lath martensite content was higher in the
F-B-M(R)TSCA condition than in the F-B-M(R)TSCA condition. In both conditions, vanadium carbide precipitates could be seen
after annealing. Fatigue-tested F-B-M(F)TSCA microstructure up to a total strain amplitude of 0.4 pct and F-B-M(F)TSCA microstructure
up to a total strain amplitude of 0.55 pct were stable. Lath martensite did not undergo deformation and in both microstructural
conditions dislocation cell structures were not observed in the ferrite or bainite regions. The interlath retained austenite
strips/films played a significant role in preventing the softening during fatigue loading. First, it was stable up to a total
strain amplitude of 0.4 and 0.55 pct in the respective microstructures. Second, it underwent heavy deformation during fatigue
loading at high total strain amplitudes, thereby accommodating the strain. Fatigue-tested F-B-M(F)TSCA microstructure at a
total strain amplitude of 0.7 pct and F-B-M(R)TSCA microstructure at a total strain amplitude of 0.8 pct revealed deformed
bainite/martensite laths, dislocation cells, and slip bands in the ferrite regions, which are characteristic features of cyclic
softening. The retained austenite transformed to martensite through a strain-induced transformation mechanism and, at that
stage, the microstructure contained in addition dislocation-rich bainite and ferrite. 相似文献
3.
S. Giribaskar Gouthama R. Prasad J. Ramkumar 《Transactions of the Indian Institute of Metals》2008,61(2-3):173-176
Equal Channel Angular Extrusion (ECAE) is a promising severe plastic deformation (SPD) process which can produce polycrystalline materials with ultra-fine grains (UFG) of sub micrometer range or nanometer range. Large plastic shear deformation induced by the high applied pressure in ECAE material processing is the prime reason behind the grain refinement. The focus of the present work is to study the evolution of dislocation microstructure during dynamic recovery (due to intense strain deformation) and static recovery (due to static annealing after deformation) in commercial Al-3%Mg alloy processed by ECAE. It is observed that local concentrations of shear strain can take place and high angle boundary (HAGB) segments are formed initially at random locations. When thermal energy is provided, during static annealing, the boundary segments get further defined and extended. This leads to the formation of very fine size grains with high mis-orientations which subsequently develop into an ultra-fine grain distribution in the material. Also, it appears dynamic recrystallisation (DRX) occurring during the deformation itself is a general phenomenon leading to refinement of grains. Transmission Electron Microscopy (TEM) is the characterizing tool used in the present study. The influence of precipitates/second phase particles on the deformation characteristics and on the increased degree of grain fragmentation is also detailed. 相似文献
4.
Superplastic behavior of a solution treated and friction stir processed (FSP) AZ91C alloy is studied. These studies are conducted in the temperature range of 300–375 °C and strain rates (SRs) in the range of 1 × 10?4–3 × 10?3 s?1. Microstructural stability of the FSP alloy is also studied in comparison to the AZ31, AZ61, and AZ91 alloys processed by various routes. High SR sensitivity in the range of 0.33–0.39 and grain size stability till 350 °C is observed for the FSP alloy. The FSP AZ91C alloy showed better thermal stability in comparison to AZ31 and AZ61 alloys. Kinetics of superplastic deformation of the FSP alloy is found to be slower as compared to AZ31 and AZ61 alloys processed by various routes, which is due to the presence of significant amount of second phase precipitates, such as, β-Mg17(Al,Zn)12, Mg2Si, and Al8Mn5 in the FSP alloy. However, these precipitates contributed for better thermal stability of the microstructure of FSP AZ91C alloy. 相似文献
5.
Bikas C. Maji Madangopal Krishnan M. Sujata Gouthama Ranjit K. Ray 《Metallurgical and Materials Transactions A》2013,44(1):172-185
The effect of Co addition has been studied in Fe-30Mn-6Si-xCo (x = 0 to 9 wt pct) shape memory alloys in terms of their microstructure, martensitic transformation and shape recovery. Microstructural investigations reveal that in Fe-Mn-Si-Co alloys, the microstructure remains single-phase austenite (??) up to 5 pct Co and beyond that becomes two-phase comprising ?? and off-stoichiometric (Fe,Co)5Mn3Si2 intermetallic ??-phases. The forward ??-?? martensite transformation start temperature (M S) decreases with the addition of Co up to 5 pct, and alloys containing more than 5 pct Co, show slightly higher M S possibly on account of two-phase microstructure. Unlike M S, the ??-?? reverse transformation start temperature (A S) has been found to remain almost unaltered by Co addition. In general, addition of Co to Fe-Mn-Si alloys deteriorates shape recovery due to decreasing resistance to plastic yielding concomitant with the formation of stress induced ?? martensite. However, there is an improvement in shape recovery beyond 5 pct Co addition, possibly due to the strengthening effect arising from the presence of (Fe,Co)5Mn3Si2 precipitates within the two-phase microstructure and due to higher amount of stress induced ?? martensite. 相似文献
6.
Thanganadar Ashokkumar Arunachalam Rajadurai Gouthama Linda L. Hussami 《The International Journal of Advanced Manufacturing Technology》2013,65(9-12):1201-1213
Mechanical alloying through high-energy ball milling was used in the production of Ni–Fe alloy powders from elemental Ni and Fe powders of average particle size 80 and 25 μm, respectively. High-energy planetary ball milling at room temperature was performed for various time durations ranging between 2 and 100 h. SPS apparatus was used for sintering of powder particles. Density of all specimens was reported and a maximum densification of 99 % was achieved in 50 wt.% Ni–Fe milled for 16 h prior to spark plasma sintering at 1,223 K. 相似文献
7.
Alloy design criteria to produce ductile phosphoric irons have been proposed based on a detailed microstructural study of
ancient Indian irons. The alloy design aims at avoiding phosphorus segregation to the grain boundaries by (a) soaking the
phosphoric iron at high temperatures within the ferrite + austenite region to precipitate austenite allotriomorphs, (b) utilizing
a critical amount of carbon to segregate to grain boundaries, and (c) precipitation of some of the phosphorus in solid solution
in the ferrite matrix as fine coherent phosphide precipitates. 相似文献
8.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献
9.
The effect of trace addition of Sn on the ageing characteristics of Al-0.7% Mg2Si has been studied by hardness measurements and transmission electron microscopy. The changes observed in the microstructural features have been explained on the basis of the strong interaction existing between Sn atoms and quenched-in vacancies. At ageing temperatures below 200°C Sn addition brings about a ratardation in the kinetics of G.P. zone growth whereas at higher ageing temperatures, it aided the precipitate nucleation and growth. The hardness data agree well with the deductions based on observations made on the thin foils. 相似文献
10.
S. Sankaran G. Malakondaiah Gouthama S. Sangal K. A. Padmanabhan 《Metallurgical and Materials Transactions A》2006,37(4):1191-1200
A multiphase ferrite-bainite-martensite (F-B-M) microstructure was developed in an automotive grade V-bearing medium carbon
microalloyed steel, 38MnSiVS5. It was characterized using optical, scanning, and transmission electron microscopy. The tensile,
Charpy impact, and static and dynamic fracture toughness behaviors were evaluated. The results are compared with those of
ferrite-pearlite (F-P) and tempered martensite (T-M) microstructures of the same steel. Although the tensile properties of
the multiphase microstructures were superior, the Charpy impact and static and dynamic fracture toughness properties were
inferior compared with those of the other two microstructures. The F-P condition displayed the highest plane strain fracture
toughness value (KIC), while the T-M condition was characterized by the highest dynamic fracture toughness (conditional) value (KIDQ). The Charpy impact energy of the T-M condition was greater than that for the other two conditions. An examination of the
surfaces of fractured samples revealed predominant ductile crack growth in the F-P microstructure and a mixed mode (ductile
and brittle) crack growth in the T-M and the F-B-M microstructures. Although the Charpy impact energy, plane fracture toughness
(KIC), and conditional dynamic fracture toughness (KIDQ) of the multiphase microstructure were inferior to those of the T-M and the F-P microstructures, the toughness properties
were comparable to those of medium carbon low alloy steels having bainite-martensite (AISI 4340) or tempered martensite microstructures. 相似文献