A TEM study of the effect of oxygen on nanocavity formation and precipitation in rapid - solidified Fe-16Ni-9Cr stainless steels

1994 ◽  
Vol 52 ◽  
pp. 700-701
Author(s):  
S. Wisutmethangoon ◽  
T. F. Kelly ◽  
J.E. Flinn
Keyword(s):  
Stainless Steels ◽  
High Mobility ◽  
Hot Extrusion ◽  
Extrusion Ratio ◽  
Gas Atomization ◽  
Cavity Formation ◽  
Nucleation Sites ◽  
Heat Treated ◽  
Different Types ◽  
Effect Of Oxygen

Vacancies are introduced into the crystal phase during quenching of rapid solidified materials. Cavity formation occurs because of the coalescence of the vacancies into a cluster. However, because of the high mobility of vacancies at high temperature, most of them will diffuse back into the liquid phase, and some will be lost to defects such as dislocations. Oxygen is known to stabilize cavities by decreasing the surface energy through a chemisorption process. These stabilized cavities, furthermore, act as effective nucleation sites for precipitates to form during aging. Four different types of powders with different oxygen contents were prepared by gas atomization processing. The atomized powders were then consolidated by hot extrusion at 900 °C with an extrusion ratio 10,5:1. After consolidation, specimens were heat treated at 1000 °C for 1 hr followed by water quenching. Finally, the specimens were aged at 600 °C for about 800 hrs. TEM samples were prepared from the gripends of tensile specimens of both unaged and aged alloys.

scholarly journals Analysis of Nanometer-Scale Precipitation in a Rapidly Solidified Stainless Steel

1997 ◽  
Vol 3 (S2) ◽  
pp. 981-982
Author(s):  
S. Wisutmethangoon ◽  
T.F. Kelly ◽  
P.P. Camus ◽  
J.E. Flinn ◽  
D.J. Larson ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Stainless Steels ◽  
Hot Extrusion ◽  
High Strength ◽  
Gas Atomization ◽  
Precipitate Morphology ◽  
Heat Treated ◽  
Wide Range ◽  
Rapidly Solidified ◽  
Corrosion And Oxidation

Though stainless steels are important technologically for a wide range of applications, they are not generally known for their very high strength. We have rapid-solidification-processed many stainless steels by gas atomization and achieved strength improvements of over 50% relative to conventionally-processed stainless steels with concomitant improvement in corrosion and oxidation behavior. These strength improvements are most pronounced after aging treatments when elevated concentrations of oxygen and vanadium are present in the stainless steel. An austenitic (FCC) stainless steel (Fe-16%Ni-9%Cr-0.5%Mn-0.2%V-0.0137%N-0.008%O by weight) was prepared by gas atomization and consolidated by hot extrusion at 900°C. These specimens were heat treated for 1 hour at 1000°C and aged at 600°C for 500 hours.The microstructure of each alloy composition was observed in TEM with bright field imaging. After aging, most alloys showed the same precipitate morphology as before aging. An obvious change, however, was found only in the alloy with highest oxygen content.

scholarly journals Complementary Use of APFIM and TEM for a Study of Precipitation in a Rapidly Solidified Stainless Steel

1997 ◽  
Vol 3 (S2) ◽  
pp. 683-684
Author(s):  
T. F. Kelly ◽  
S. Wisutmethangoon ◽  
P. P. Camus ◽  
D. J. Larson ◽  
M. K. Miller
Keyword(s):  
Stainless Steels ◽  
Hot Extrusion ◽  
High Strength ◽  
Dark Field ◽  
Environmental Stability ◽  
Gas Atomization ◽  
Fringe Contrast ◽  
Dark Field Imaging ◽  
Wide Range ◽  
Field Imaging

Stainless steels are important technologically for a wide range of applications. Though they are attractive for their environmental stability, austenitic versions of these steels are not generally known for their very high strength. We have rapid-solidification-processed many stainless steels by gas atomization and achieved strength improvements of over 50% relative to conventionally-processed stainless steels with concomitant improvement in corrosion and oxidation behavior. These strength improvements are most pronounced when elevated concentrations of oxygen and vanadium are present in the metal and we need to know how these elements affect precipitation in the alloy.The specimen material (FCC Fe-16%Ni-9%Cr-0.5%Mn-0.2%V-0.0137%N-0.008%O by weight) was prepared by gas atomization and hot extrusion followed by precipitation aging as described elsewhere. We observed the structure in TEM and found 20 nm precipitates on dislocations, Fig. 1a. We did not observe smaller precipitates in the grain interiors using diffraction contrast bright field imaging, however, with weak-beam dark field imaging, Moiré fringe contrast is observed throughout the material, Fig. 1b.

Hot Extrusion of Nanostructured Al Alloy Powder: Extrusion Ratio and Temperature Effect on the Microstructure and Mechanical Properties

2008 ◽  
Vol 570 ◽  
pp. 91-96
Author(s):  
M.M. Peres ◽  
J.B. Fogagnolo ◽  
Fernando Audebert ◽  
F. Saporiti ◽  
Alberto Moreira Jorge ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Aluminium Alloy ◽  
Alloy Powder ◽  
Bulk Material ◽  
Hot Extrusion ◽  
Extrusion Ratio ◽  
Al Alloy ◽  
Gas Atomization ◽  
Processing Conditions ◽  
Compressive Tests

A nanostructured aluminium alloy powder, prepared by rapid solidification via gas atomization, was consolidated into bulk material under various processing conditions via hot extrusion. The microstructure modifications and mechanical properties of the consolidated alloys as a function of the extrusion conditions were investigated. The increase in the extrusion-load with the increase of extrusion-rate and decrease of temperature are shown and discussed in association with the modification in the microstructures. The differences in mechanical properties measured by compressive tests are also discussed in association with the extrusion parameters. Furthermore, suggestions are given for rationalising the extrusion ratio and temperature conditions for the consolidation of nanostructured aluminium alloy powders via hot extrusion.

Type 316l Stainless Steels Exhibiting Five-Fold Symmetry Mo-Rich Phase

1997 ◽  
Vol 3 (S2) ◽  
pp. 685-686
Author(s):  
Yong-Jun Oh ◽  
Woo-Seog Ryu ◽  
Jun-Hwa Hong ◽  
Il-Hiun Kuk
Keyword(s):  
Nitrogen Content ◽  
Stainless Steels ◽  
Aging Treatment ◽  
Rich Phase ◽  
Heat Treated ◽  
Different Types ◽  
Type 316L ◽  
Rapidly Solidified ◽  
Nitrogen Contents ◽  
Initial Results

The existence of phases exhibiting five-fold symmetry patterns has recently been reported for conventional heat treated alloys as well as rapidly solidified alloys. The present paper reports initial results on the analysis of a Mo-rich phase in 316L stainless steel which exhibits this symmetry. The formation and growth of this Mo-rich phase were investigated as a function of aging time. In addition, the effect of nitrogen content on the formation of this five-fold phase was also investigated.The materials investigated were type 316L stainless steels with nitrogen contents of 0.024% and 0.150%. The materials were solution-annealed at 1100 °C for 30 minites followed by an aging treatment at 700 °C for 10–50 hours in a vacuum sealed quartz tube. TEM samples were prepared by conventional twin-jet polishing and carbon replications extracted by use of a bromine-etch.Irrespective of nitrogen content, the grain boundary phases after 50 hours of aging were totally observed as five different types of precipitates; M23C6 and M6C carbides, intermetallic η and χ phases, and the five-fold symmetry phase.

Microstructure and Tensile Properties of Al-15wt%Mg2Si Composite after Hot Extrusion and Heat Treatment

2011 ◽  
Vol 471-472 ◽  
pp. 1171-1176 ◽  
Author(s):  
A. Bahrami ◽  
A. Razaghian ◽  
M. Emamy ◽  
H.R. Jafari Nodooshan ◽  
G.S. Mousavi
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Tensile Strength ◽  
Tensile Testing ◽  
Solution Treatment ◽  
Hot Extrusion ◽  
Extrusion Ratio ◽  
Primary Mg2si ◽  
Heat Treated ◽  
The Relationship

In this study, the relationship between microstructures and mechanical properties of the extrusion processed Al-15wt.%Mg2Si composite was investigated after applying various extrusion ratios (6:1, 12:1 and 18:1) and solution treatment. Various techniques including metallography, tensile testing and SEM fractography were utilized to characterize the mechanical behavior of the MMC. Results demonstrated that extruded and heat treated composite possesses considerably higher strength and enhanced ductility in comparison with the as-cast samples. It was also found that heat treatment and extrusion processes do not change the primary Mg2Si morphology considerably, but its size increases as extrusion ratio decreased. Heat treatment and extrusion ratio effects on tensile strength, elongation of extruded specimens were also studied in this work.

Interaction Between Dislocations and NiFe2O4 Precipitates In A NiO Matrix

1991 ◽  
Vol 230 ◽  
Author(s):  
Scott R. Summerfelt ◽  
C. Barry Carter
Keyword(s):  
Stacking Faults ◽  
Temperature Deformation ◽  
Dislocation Loops ◽  
Partial Dislocations ◽  
Nucleation Sites ◽  
Heat Treated ◽  
Dislocation Interactions ◽  
Different Types ◽  
Preferential Nucleation ◽  
Pass Through

AbstractThree different types of dislocation interactions with NiFe2O4 (spinel crystal structure) precipitates in a NiO matrix have been studied. In the first, the movement of dislocations introduced by room temperature deformation is impeded by the spinel precipitates. Glide dislocations in the NiO with ½<011> Burgers vectors and {011} glide planes cannot pass through the spinel precipitates without forming stacking faults because the perfect NiO dislocations are partial dislocations in NiFe2O4. Many dislocation loops but no stacking faults were observed in the deformed samples indicating that the gliding dislocations formed the loops when they moved past the precipitates. In the second type of interactions, cusps were formed in the spinel-NiO interface at close to the dislocation loops when the sample was heat treated; the cusps indicate preferential dissolution of the spinel. In the final interaction, the dislocations were shown to act as preferential nucleation sites when spinel was precipitated from the NiO matrix. At slow nucleation rates, NiFe2O4 precipitated only on the dislocations; when the nucleation rate was increased, precipitation occurred both on and away from the dislocations. Precipitates which form at a dislocation may contain a stacking fault extending from the partial dislocation to a cusp in the spinel-NiO interface. When this occurred, the stacking faults were observed to be faceted parallel to either {111} or {011} planes.

Carbide precipitation and chromium depletion on coherent twin boundaries in deformed 304 stainless steels

1992 ◽  
Vol 50 (2) ◽  
pp. 1216-1217
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
Interfacial Free Energy ◽  
Carbide Precipitation ◽  
Twin Boundaries ◽  
Invariant Structure ◽  
Heat Treated ◽  
Constant Structure ◽  
Cr Depletion

Coherent annealing-twin boundaries are constant structure and energy interfaces with an average interfacial free energy of ∼19mJ/m2 versus ∼210 and ∼835mJ/m2 for incoherent twins and “regular” grain boundaries respectively in 304 stainless steels (SS). Due to their low energy, coherent twins form carbides about a factor of 100 slower than grain boundaries, and limited work has also shown differences in Cr-depletion (sensitization) between twin versus grain boundaries. Plastic deformation, may, however, alter the kinetics and thermodynamics of twin-sensitization which is not well understood. The objective of this work was to understand the mechanisms of carbide precipitation and Cr-depletion on coherent twin boundaries in deformed SS. The research is directed toward using this invariant structure and energy interface to understand and model the role of interfacial characteristics on deformation-induced sensitization in SS. Carbides and Cr-depletion were examined on a 20%-strain, 0.051%C-304SS, heat treated to 625°C-4.5h, as described elsewhere.

Deformation effects on transgranular carbide precipitation in 304 stainless steels

1992 ◽  
Vol 50 (1) ◽  
pp. 260-261
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Stainless Steels ◽  
True Strain ◽  
Carbide Precipitation ◽  
Material Research ◽  
Chromium Depletion ◽  
Engineering Strain ◽  
Twin Fault ◽  
Heat Treated ◽  
Strain Induced Martensite ◽  
The Relationship

Plastic deformation is a key variable producing accelerated intergranular (IG) carbide precipitation and chromium-depletion (sensitization) development in stainless steels. Deformation above 20% also produces transgranular (TG) carbides and depletion in the material. Research on TG carbides in SS is, however, limited and has indicated that the precipitation is site-specific preferring twin-fault intersections in 316 SS versus deformation-induced martensite and martensite lath-boundaries in 304 SS. Evidences indicating the relation between martensite and carbides were, however, sketchy.The objective of this work was to fundamentally understand the relationship between TG carbides and strain-induced martensite in 304 SS. Since strain-induced martensite forms at twin-fault intersections in 304 SS and the crystallography of the transformation is well understood, we believed that it could be key in understanding mechanisms of carbides and sensitization in SS. A 0.051% C, 304 SS deformed to ∽33% engineering strain (40% true strain) and heat treated at 670°C/ 0.1-10h was used for the research. The study was carried out on a Hitachi H-8000 STEM at 200 kV.

Effect of Heat Treatment on the Microstructure and Property of TiAl Alloys Prepared by Gas Atomization Powders

2013 ◽  
Vol 747-748 ◽  
pp. 497-501
Author(s):  
Na Liu ◽  
Zhou Li ◽  
Guo Qing Zhang ◽  
Hua Yuan ◽  
Wen Yong Xu ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Heat Treatment Temperature ◽  
Tial Alloy ◽  
Lamellar Microstructure ◽  
Treatment Temperature ◽  
Gas Atomization ◽  
Thermally Induced ◽  
Heat Treated ◽  
Fine Duplex ◽  
Step Heat Treatment

Powder metallurgical TiAl alloy was fabricated by gas atomization powders, and the effect of heat treatment temperature on the microstructure evolution and room tensile properties of PM TiAl alloy was investigated. The uniform fine duplex microstructure was formed in PM TiAl based alloy after being heat treated at 1250/2h followed by furnace cooling (FC)+ 900/6h (FC). When the first step heat treatment temperature was improved to 1360/1h, the near lamellar microstructure was achieved. The ductility of the alloy after heat treatment improved markedly to 1.2% and 0.6%, but the tensile strength decreased to 570MPa and 600MPa compared to 655MPa of as-HIP TiAl alloy. Post heat treatment at the higher temperature in the alpha plus gamma field would regenerate thermally induced porosity (TIP).

Effects of High Magnetic Fields on Martensitic Transformation at Cryogenic Temperatures for Variously Heat Treated Stainless Steels

1994 ◽  
pp. 1207-1213 ◽  
Author(s):  
Koji Shibata ◽  
Yasushi Kurita ◽  
Tsutomu Shimonosono ◽  
Yoshiaki Murakami ◽  
Satoshi Awaji ◽  
...  
Keyword(s):  
Martensitic Transformation ◽  
Magnetic Fields ◽  
Stainless Steels ◽  
High Magnetic Fields ◽  
Cryogenic Temperatures ◽  
Heat Treated
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