A Review of Creep of Silicides and Composites

1993 ◽  
Vol 322 ◽  
Author(s):  
K. Sadananda ◽  
C.R. Feng
Keyword(s):  
Grain Size ◽  
Creep Resistance ◽  
Volume Fraction ◽  
Dominant Role ◽  
Ceramic Composites ◽  
High Temperature Materials ◽  
Power Law Creep ◽  
Creep Regime ◽  
Very High ◽  
High Creep Resistance

AbstractA review of creep behavior of molybdenum disilicides and their composites is presented. Creep rates of these silicides are compared with those of other high temperature materials such as superalloys, ceramic-ceramic composites, intermetallics including aluminides (nickel and titanium), berylides (vanadium and niobium), and refractory metals(molybdenum and tungsten). Creep rates of silicides are shown to be very sensitive to grain size even in the power-law creep regime with grain size exponent of the order of five and above. In addition, the results show that with increase in volume fraction of reinforcements there is a decrease in creep rates for volume percentages less than 25%. To achieve significant improvement in creep strength volume percentages of reinforcements greater than 25% are required. This weakening effect at low volume percentages is related to accompanying decrease in grain size with the addition of reinforcements. Addition of carbon to MoSi2 eliminated the silica present at grain boundaries and converted it to SiC. The SiC thus formed, inhibited grain growth during hot pressing. Thus although addition of carbon enhanced creep resistance, its effect is masked by the accompanying decrease in grain size. Thus, grain size plays a dominant role in the creep of molydisilicide composites. It is shown that among all the materials molybdenum disilicides possess very high creep resistance comparable to ceramic-ceramic composites.

TIMKEN 16-15-6

Alloy Digest ◽  
1963 ◽  
Vol 12 (12) ◽  
Keyword(s):  
Mechanical Properties ◽  
Creep Resistance ◽  
Elevated Temperatures ◽  
Roller Bearing ◽  
Heat Treating ◽  
Resistant Steel ◽  
Heat Resistant Steel ◽  
Corrosion And Oxidation ◽  
Very High ◽  
High Creep Resistance

Abstract Timken 16-15-6 is a non-magnetic, austenitic, corrosion and heat resistant steel having high creep resistance at elevated temperatures and good corrosion and oxidation resistance. It age-hardens at elevated temperatures after solution quenching, and possesses very high mechanical properties. This datasheet provides information on composition, microstructure, hardness, and tensile properties as well as creep. It also includes information on forming, heat treating, machining, and joining. Filing Code: SS-150. Producer or source: Timken Roller Bearing Company.

Microstructure-Property Relationships of Two Ti2AlNb-based Intermetallic Alloys: Ti-15Al-33Nb(at.%) and Ti-21Al-29Nb(at.%)

2004 ◽  
Vol 842 ◽  
Author(s):  
Christopher J. Cowen ◽  
Dingqiang Li ◽  
Carl J. Boehlert
Keyword(s):  
Grain Size ◽  
Creep Resistance ◽  
Volume Fraction ◽  
Ductile Failure ◽  
Phase Volume ◽  
Phase Volume Fraction ◽  
Al Content ◽  
Creep Stress ◽  
Heat Treated ◽  
Elongation To Failure

ABSTRACTTwo Ti2AlNb intermetallic orthorhombic (O) alloys, Ti-15Al-33Nb and Ti-21Al-29Nb(at.%), were subtransus processed into sheets, using pancake forging and hot-pack rolling, and evaluated in tension (25 and 650°C) and creep (650–710°C) and the properties and deformation behavior were related to microstructure. Some of the microstructural features evaluated were grain boundary character, grain size, phase volume fraction, and morphology. The alloy Al content was important to strength and elongation-to-failure (εf), where higher Al contents lead to greater tensile strengths and lower εf values and a corresponding brittle fracture response. However, the room temperature (RT) strengths of Ti-15Al-33Nb, which exhibited greater BCC phase volume fractions than Ti-21Al-29Nb and ductile failure (εf >2%), were always greater than 775 MPa. The creep stress exponents (n) and activation energies (Qapp) suggested that a transition in the dominant creep deformation mechanism exists and is dependent on stress and microstructure. Supertransus heat treatment, which increased the prior-BCC grain size and resulted in a lath-type O+BCC microstructure, resulted in reduced creep strains and strain rates. In fact, the supertransus heat-treated Ti-15Al-33Nb microstructures exhibited greater creep resistance than subtransus heat-treated Ti-21Al-29Nb microstructures. Combining the creep observations with the tensile response, the supertransus heat treated Ti-15Al-33Nb lath O+BCC microstructures exhibited the most attractive combination of tensile strength, εf values, and creep resistance.

Grain size effects in nanocrystalline materials

1992 ◽  
Vol 7 (8) ◽  
pp. 2114-2118 ◽  
Author(s):  
C. Suryanarayana ◽  
D. Mukhopadhyay ◽  
S.N. Patankar ◽  
F.H. Froes
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Size Effects ◽  
Nanocrystalline Materials ◽  
Volume Fraction ◽  
High Hardness ◽  
Careful Analysis ◽  
Grain Sizes ◽  
Critical Grain Size ◽  
Very High

Nanocrystalline materials have a grain size of only a few nanometers and are expected to possess very high hardness and strength values. Even though the hardness/strength is expected to increase with a decrease in grain size, recent observations have indicated that the hardness increases in some cases and decreases in other cases. A careful analysis of the available results on the basis of existing models suggests that there is a critical grain size below which the triple junction volume fraction increases considerably over the grain boundary volume fraction and this is suggested to be responsible for the observed softening at small grain sizes.

Effect of carbon nanotubes on the microstructure and fracture resistance of nanostructured oxide ceramics

2021 ◽  
pp. 21-26
Author(s):  
Yu.A. Mirovoy ◽  
◽  
A.G. Burlachenko ◽  
A.S. Buyakov ◽  
E.S. Dedova ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanotubes ◽  
Grain Size ◽  
Fracture Resistance ◽  
Zirconium Dioxide ◽  
Volume Fraction ◽  
Stable State ◽  
Ceramic Composites ◽  
Plasma Sintering ◽  
Nanostructured Oxide

The structure and properties of ceramics based on zirconium dioxide stabilized yttrium oxide with the addition of high-modulus inclusions of carbon nanotubes were investigated. The composite materials were obtained by spark plasma sintering. The introduction of carbon nanotubes provides a slight decrease in the density and grain size of ceramics. Growth of volume fraction of carbon nanotubes leads to increase of mechanical properties of ceramic composites. The highest values of mechanical properties were obtained by the introduction of 5 vol.% of carbon nanotubes and were E = (246±8) GPa, H = (12.7±0.21) GPa, K 1 CI = (12.1±0.35) MPa∙m1/2, K 1 CN = (7.8±0.29) MPa∙m1/2. The increase of fracture toughness when carbon nanotubes are introduced into the ceramic matrix is caused by two dissipative mechanisms - phase transformation from tetragonal to monoclinic modification of ZrO2 and crack bridging. As the amount of introduced additive increases, the contribution of martensitic transformation in fracture resistance decreases, which is associated with a decrease in the grain size of the tetragonal zirconium dioxide phase and, accordingly, its transition to a stable state.

scholarly journals Microstructural evolution during high-temperature tensile creep at 1,500°C of a MoSiBTiC alloy

2020 ◽  
Vol 39 (1) ◽  
pp. 136-145 ◽  
Author(s):  
Sojiro Uemura ◽  
Shiho Yamamoto Kamata ◽  
Kyosuke Yoshimi ◽  
Sadahiro Tsurekawa
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Microstructural Evolution ◽  
Grain Boundary Sliding ◽  
Primary Creep ◽  
Tensile Creep ◽  
Tertiary Creep ◽  
Continuous Dynamic Recrystallization ◽  
Continuous Dynamic ◽  
Creep Regime

AbstractMicrostructural evolution in the TiC-reinforced Mo–Si–B-based alloy during tensile creep deformation at 1,500°C and 137 MPa was investigated via scanning electron microscope-backscattered electron diffraction (SEM-EBSD) observations. The creep curve of this alloy displayed no clear steady state but was dominated by the tertiary creep regime. The grain size of the Moss phase increased in the primary creep regime. However, the grain size of the Moss phase was found to remarkably decrease to <10 µm with increasing creep strain in the tertiary creep regime. The EBSD observations revealed that the refinement of the Moss phase occurred by continuous dynamic recrystallization including the transformation of low-angle grain boundaries to high-angle grain boundaries. Accordingly, the deformation of this alloy is most likely to be governed by the grain boundary sliding and the rearrangement of Moss grains such as superplasticity in the tertiary creep regime. In addition, the refinement of the Moss grains surrounding large plate-like T2 grains caused the rotation of their surfaces parallel to the loading axis and consequently the cavitation preferentially occurred at the interphases between the end of the rotated T2 grains and the Moss grains.

scholarly journals Three Regions in the Power-Law Creep Regime of TiAl

1992 ◽  
Vol 33 (12) ◽  
pp. 1182-1184 ◽  
Author(s):  
Yukio Ishikawa ◽  
Kouichi Maruyama ◽  
Hiroshi Oikawa
Keyword(s):  
Power Law ◽  
Power Law Creep ◽  
Creep Regime

Microstructural Control of Ductile Crack Propagation in TMCP HSLA Pipeline Steels

2014 ◽  
Vol 922 ◽  
pp. 568-573
Author(s):  
Victor Carretero Olalla ◽  
N. Sanchez Mouriño ◽  
Philippe Thibaux ◽  
Leo Kestens ◽  
Roumen H. Petrov
Keyword(s):  
Grain Size ◽  
Crack Propagation ◽  
Volume Fraction ◽  
Main Role ◽  
Charpy Test ◽  
Initiation And Propagation ◽  
Average Grain Size ◽  
Main Disadvantage ◽  
Steel Grades ◽  
Increasing Demand

Control of ductile fracture propagation is one of the major concerns for pipeline industry, particularly with the increasing demand of new control rolled steel grades required to maintain integrity at high operational pressures. The objective of this research is to understand which microstructural features govern crack propagation, and to analyse the effect of two of them (average grain size, and volume fraction of pearlite). The main disadvantage during classical Charpy test was to discriminate the crack initiation and propagation energy during fracture of a notched sample. The initiation appears to be caused by the stress state in the neighbouring of Ti-containing precipitates or pearlite particles (no presence of M/A constituents or MnS inclusions was detected in the evaluated grades), propagation-arrest of the crack is assumed to play the main role concerning the control of fracture. Our approach to characterize the fracture resistance is to measure the energy absorbed during the crack propagation stage by means of load-displacement curves obtained via instrumented Charpy test. It was observed that the energy absorbed during crack propagation is not influenced by the average grain size but by the fraction and the morphological (banded-not banded) distribution of second pearlitic phase. This suggests that a different approach to characterize the heterogeneities in grain size clustering might be followed to correlate the energy measured during crack propagation and the morphological features of the steel.

Study on Dynamic Recrystallization Behavior in Deformed Austenite of 52100 Steel by Using JMAK-Model

2013 ◽  
Vol 275-277 ◽  
pp. 1833-1837
Author(s):  
Ke Lu Wang ◽  
Shi Qiang Lu ◽  
Xin Li ◽  
Xian Juan Dong
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Hot Deformation ◽  
Volume Fraction ◽  
True Strain ◽  
Strain And Strain Rate ◽  
Average Grain Size ◽  
Dynamic Recrystallization Behavior ◽  
Simulation And Experiment ◽  
Good Agreement

A Johnson-Mehl-Avrami-Kolmogorov (JMAK)-model was established for dynamic recrystallization in hot deformation process of 52100 steel. The effects of hot deformation temperature, true strain and strain rate on the microstructural evolution of the steel were physically studied by using Gleeble-1500 thermo-mechanical simulator and the experimental results were used for validation of the JMAK-model. Through simulation and experiment, it is found that the predicted results of DRX volume fraction, DRX grain size and average grain size are in good agreement with the experimental ones.

scholarly journals A Dislocation-Based Theory for the Deformation Hardening Behavior of DP Steels: Impact of Martensite Content and Ferrite Grain Size

2010 ◽  
Vol 2010 ◽  
pp. 1-16 ◽  
Author(s):  
Yngve Bergström ◽  
Ylva Granbom ◽  
Dirk Sterkenburg
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Deformation Process ◽  
Volume Fraction ◽  
High Energy ◽  
Martensite Content ◽  
Plastic Deformation Process ◽  
Deformation Hardening ◽  
Dp Steels ◽  
Ferrite Grain Size

A dislocation model, accurately describing the uniaxial plastic stress-strain behavior of dual phase (DP) steels, is proposed and the impact of martensite content and ferrite grain size in four commercially produced DP steels is analyzed. It is assumed that the plastic deformation process is localized to the ferrite. This is taken into account by introducing a nonhomogeneity parameter, f(ε), that specifies the volume fraction of ferrite taking active part in the plastic deformation process. It is found that the larger the martensite content the smaller the initial volume fraction of active ferrite which yields a higher initial deformation hardening rate. This explains the high energy absorbing capacity of DP steels with high volume fractions of martensite. Further, the effect of ferrite grain size strengthening in DP steels is important. The flow stress grain size sensitivity for DP steels is observed to be 7 times larger than that for single phase ferrite.

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