The Effect of Second Phase Properties on the Compression Creep Behavior of MoSi2 Composites

1992 ◽  
Vol 273 ◽  
Author(s):  
A. K. Ghosh ◽  
A. Basu ◽  
H. Kung
Keyword(s):  
Grain Size ◽  
Creep Behavior ◽  
Creep Strength ◽  
Relative Strength ◽  
Second Phase ◽  
Compression Creep ◽  
Phase Properties

ABSTRACTIn an effort to enhance the toughness and creep strength of MoSi2, the role of various metallic and ceramic reinforcements is being examined. In this work, the effects of an oxide, a carbide and a nitride reinforcement on the compression creep behavior of MoSi2 are explored. Variations in the deformability of reinforcements and their relative strength and flaw population appear to influence the creep strength of the composites. Refinements in grain size also improve crack tolerance of the composite during deformation at 1200°C.

Processing iron aluminides by heavy deformation for improved room temperature strength-ductility and for high temperature creep strength

2011 ◽  
Vol 1295 ◽  
Author(s):  
David G. Morris ◽  
Maria Antonia Muñoz-Morris
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
High Temperature ◽  
Severe Plastic Deformation ◽  
Creep Strength ◽  
Room Temperature ◽  
High Strain ◽  
Iron Aluminides ◽  
Al Alloy ◽  
Second Phase

ABSTRACTIron aluminides show many interesting properties, but still show relatively poor ductility at room temperature and only moderate creep resistance at temperatures above about 600ºC. Processes of severe plastic deformation have been investigated for a wide range of ductile alloys over the past decade, but have hardly been considered for intermetallics. This presentation discusses two studies aimed at refining microstructure by the use of severe plastic deformation of iron aluminides. The first considers processing Fe3Al by heavy cold rolling, followed by annealing for recovery or recrystallization, with an objective of refining grain size to improve strength at the same time as ductility. The high strength and poor ductility of the work hardened material leads to a danger of cracking during rolling, which is a problem for manufacturing large quantities of healthy material. Suitable rolling and recovery treatments can, nevertheless, lead to strong materials with some plastic ductility. A different technique of multidirectional, high-strain and high-temperature forging applied to a boride-containing Fe3Al alloy produces a material with large grain size and refined dispersion of boride particles. These particles lead to a considerable increase in creep strength under conditions of moderate stresses at temperatures around 700ºC. This high-strain forging technique can be seen as an intermediate processing method between conventional wrought metallurgy and mechanical-alloying powder metallurgy. This technique offers the possibility to improve high temperature behaviour of such intermetallics containing second-phase dispersions, and can be scaled to produce large quantities of high-quality material.

High temperature creep strength in a nanodispersion-strengthened ferritic alloy prepared by heavy plastic deformation

2011 ◽  
Vol 1298 ◽  
Author(s):  
David G. Morris ◽  
Maria Antonia Muñoz-Morris
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
High Temperature ◽  
Creep Strength ◽  
High Strain ◽  
Ferritic Steels ◽  
Al Alloy ◽  
Second Phase ◽  
Corrosion Properties ◽  
Wide Range

ABSTRACTProcesses of severe plastic deformation have been investigated for a wide range of ductile alloys over the past decade, generally with an objective of refining the microstructural scale, for example the grain size, but have hardly been considered for intermetallics. This presentation discusses processing of a boride-containing Fe3Al alloy using a multidirectional, high-strain and high-temperature forging technique. Iron aluminides with relatively low Al contents can be regarded as Al-rich ferritic steels with outstanding oxidation-corrosion properties. However, as for many ferritic steels, they show poor creep resistance at temperatures above about 600ºC. The deformation processing leads to a material with large grain size and refined dispersion of thermally-stable boride particles. The particles produce a large increase in creep strength under conditions of moderate stresses and low strain rates at temperatures near 700ºC. This high-strain forging technique can be seen as an intermediate processing method between conventional wrought metallurgy and mechanical-alloying powder metallurgy, whereby an initially coarse and inhomogeneous dispersion of second phase is refined and made more homogeneous, and can be considered as a useful processing technique for a wide range of particle-containing materials.

The Role of Crystallization of an Intergranular Glassy Phase in Determining Grain Boundary Residual Stresses in Debased Aluminas

1989 ◽  
Vol 170 ◽  
Author(s):  
Nitin P. Padture ◽  
Helen M. Chan ◽  
Brian R. Lawn ◽  
Michael J. Readey
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Residual Stresses ◽  
Glassy Phase ◽  
Analytical Techniques ◽  
Ceramic Materials ◽  
Strength Test ◽  
Second Phase

AbstractThe influence of microstructure on the crack resistance (R-curve) behavior of a commercial debased alumina containing large amounts of glassy phase (28 vol %) has been studied using the Indentation-Strength test. The effect of two microstructural variables, viz. grain size and the nature of the intergranular second phase (glassy or crystalline) has been evaluated. Crystallization of the intergranular glass was carried out in order to generate residual stresses at the grain boundaries, which have been shown to enhance R-curve behavior in ceramic materials. Enhancement of the R-curve behavior was observed with the increase in grain size. However, no effect of the nature of the intergranular second phase on the R-curve behavior, in small and large grain materials, was observed. The results from characterization of these materials using various analytical techniques is presented, together with possible explanations for the observed effects.

Effect of Er2O3 on the Microstructure and Electrical Properties of (Er, Ta)-Doped Tio2 Capacitor-Varistor Ceramics

2011 ◽  
Vol 216 ◽  
pp. 563-567
Author(s):  
Tian Guo Wang ◽  
Qun Qin ◽  
Dong Jian Zhou
Keyword(s):  
Grain Size ◽  
Rare Earth ◽  
Electrical Properties ◽  
Grain Boundary ◽  
Breakdown Voltage ◽  
Nonlinear Coefficient ◽  
Rare Earth Oxide ◽  
Second Phase ◽  
Barrier Model

TiO2-based capacitor-varistor ceramics doped with Er2O3 were prepared and the microstructures and nonlinear electrical properties were investigated. The results show that there exist second phase Er2TiO3 on the surface of TiO2 grains. The grain size was found to decrease with increasing Er2O3 content. The addition of rare earth oxide Er2O3 leads to increase the nonlinear coefficient and the breakdown voltage. It was found that the nonlinear coefficient presents a peak of α = 4.5 for the sample doped with 1.1 mol% Er2O3, which isconsistent with the highest grain boundary in the composition. In order to illustrate the role of grain boundary barriers for TiO2-Ta2O5-Er2O3 varistors, a grian boundary defect barrier model was introduced.

Particle and grain size effects on the dielectric behavior of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3

1990 ◽  
Vol 5 (12) ◽  
pp. 2902-2909 ◽  
Author(s):  
Philippe Papet ◽  
Joseph P. Dougherty ◽  
Thomas R. Shrout
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Grain Growth ◽  
Morphological Changes ◽  
Dielectric Behavior ◽  
Relaxor Ferroelectric ◽  
Liquid Phase Sintering ◽  
Second Phase ◽  
Scaling Effects

The role of particle and grain size on the dielectric behavior of the perovskite relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 [PMN] was investigated. Ultrafine powders of PMN were prepared using a reactive calcination process. Reactive calcination, the process by which morphological changes take place upon reaction of the component powders, produced particle agglomerates less than 0.5 μm. Through milling, these structures were readily broken down to ∼70 nanometer-sized particulates. The highly reactive powders allowed densification as low as 900 °C, but with corresponding grain growth in the micron range. Such grain growth was associated with liquid phase sintering as a result of PbO–Nb2O5 second phase(s) pyrochlore. Sintering, assisted by hot uniaxial pressing, below the temperature of liquid formation of 835 °C, allowed the fabrication of highly dense materials with a grain size less than 0.3 μm. The dielectric and related properties were determined for samples having grain sizes in the range of 0.3 μm to 6 μm. Characteristic of relaxors, frequency dependence (K and loss) and point of Tmax were found to be related to grain and/or particle size and secondarily to the processing conditions. Modeling of particle size/dielectric behavior was performed using various dielectric properties of 0–3 composites comprised of varying size powder in a polymer matrix. An intrinsic-microdomain perturbation concept was proposed to interpret observed scaling effects of the relaxor dielectric behavior in contrast to normally accepted extrinsic grain boundary models.

The Role of Boron in the Mechanical Milling of Titanium-6 %Aluminium-4% Vanadium Powders

1999 ◽  
Vol 581 ◽  
Author(s):  
A.P. Brown ◽  
R. Brydson ◽  
C. Hammond ◽  
T.M.T. Godfrey ◽  
A. Wisbey
Keyword(s):  
Grain Size ◽  
Mechanical Milling ◽  
Volume Fraction ◽  
Microstructural Development ◽  
Second Phase ◽  
Local Concentration ◽  
Fine Grained ◽  
Particle Form ◽  
Particulate Reinforced

ABSTRACTThe reduction in grain size of a metal can lead to significant improvement in mechanical properties. Mechanical alloying (MA) with a second phase is a possible route to producing fine-grained, particulate reinforced material. This study describes the microstructural development of Ti-6%Al-4%V milled with increasing concentrations of boron. Mechanical milling of Ti-6%Al-4%V powder produces a nanocrystalline material. MA of Ti-6%Al-4%V with boron results in the alloying of the two to form either a boride or an amorphous phase when the local concentration of boron is ∼ 50 at.%. During milling, the boron tends to remain near to its original particle form and in these boron-rich regions TiB is formed. Beyond these regions small amounts of boron (a few at.%) mix with the titanium matrix and reduce further the grain size of the titanium. An increase in the global concentration of boron increases the volume fraction of boride produced.

Structure of second phases in TiAl alloys containing Cr and B

1991 ◽  
Vol 49 ◽  
pp. 576-577
Author(s):  
Ernest L. Hall ◽  
Shyh-Chin Huang
Keyword(s):  
Grain Size ◽  
Second Phase ◽  
Structure And Properties ◽  
Tial Alloys ◽  
Second Phases ◽  
Interstitial Elements

Addition of interstitial elements to γ-TiAl alloys is currently being explored as a method for improving the properties of these alloys. Previous work in which a number of interstitial elements were studied showed that boron was particularly effective in refining the grain size in castings, and led to enhanced strength while maintaining reasonable ductility. Other investigators have shown that B in γ-TiAl alloys tends to promote the formation of TiB2 as a second phase. In this study, the microstructure of Bcontaining TiAl alloys was examined in detail in order to describe the mechanism by which B alters the structure and properties of these alloys.

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