Observation of slip propagation across grain boundaries in Ni3Al

1986 ◽  
Vol 44 ◽  
pp. 864-865 ◽  
Author(s):  
I. Baker ◽  
E.M. Schulson ◽  
J.A. Horton
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Room Temperature ◽  
Size Dependence ◽  
Direct Evidence ◽  
Specimen Preparation ◽  
Fine Grained ◽  
Room Temperature Yield Strength ◽  
Pile Up ◽  
Preparation Techniques

Recent modelling of the grain size dependence of the room-temperature yield strength of Ni3Al has invoked the concept of dislocation pile-ups. The idea is that the yield strength measured in the Liiders regime (i.e. the Liiders band propagation stress) represents not the stress to independently nucleate slip in each grain but the stress required to propagate slip through the material. This paper presents direct evidence of slip propagation from one grain to the next and thus validation of the use of a pile-up model for Ni3Al.Miniature tensile specimens (3 mm x 7 mm x0.2 mm), made from an extruded rod of fine-grained (∽10 μm) Ni3Al containing 0.35 at.% boron, were strained under tension whilst being observed in a Philips EM 430T operated at 300 KV. Details of the design and operation of the straining stage and of the specimen preparation techniques are given elsewhere.

Grain Size Dependence of Tensile Properties in Cu-Sn Thin Foils (Experimental Study)

2015 ◽  
Vol 736 ◽  
pp. 19-23
Author(s):  
Taek Kyun Jung ◽  
Hyo Soo Lee ◽  
Hyouk Chon Kwon
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Experimental Study ◽  
Grain Size ◽  
Yield Strength ◽  
Room Temperature ◽  
Size Dependence ◽  
Yield Drop ◽  
Thin Foils ◽  
Vacuum Atmosphere

This study was carried out to investigate the effects of grain size on mechanical properties in Cu-Sn foil with a thickness of 30 um. The grain size was varied from approximately 7 um to 50 um using heat treatment at 773 K for 2 h to 24 h in a vacuum atmosphere. Tensile test was carried out at room temperature with strain rate of 1mm/min. Typical yield drop phenomenon was observed. Mechanical properties were found to be strongly affected by microstructural features including grain size. The yield strength and tensile strength gradually decreased with increasing the grain size. The strain to fracture also decreased by grain growth. These results could be explained by not only the grain size dependence of yield strength but also the ratio of thickness to grain size dependence of yield strength.

The Strength and Ductility of Intermetallic Compounds: Grain Size Effects

1986 ◽  
Vol 81 ◽  
Author(s):  
E.M. Schulson ◽  
I. Baker ◽  
H.J. Frost
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Intermetallic Compounds ◽  
Size Effects ◽  
Nickel Aluminide ◽  
Marked Reduction ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
The Relationship ◽  
Strength And Ductility

Since writing on this subject two years ago [1], a number of developments have occurred, particularly in relation to the mechanical properties of the L12 nickel aluminide Ni3Al. Some elucidate the nature of the yield strength and the extraordinarily beneficial effect of boron on low-temperature ductility. Some others expose, at least in part, the nature of the marked reduction in ductility at elevated temperatures. Another considers the mechanisms dominating creep deformation. Also during this period, contradictions have appeared: the relationship between the yield strength and the grain size, d, at room temperature has been contested, and opposing views of grain refinement on ductility have been reported.This paper reviews these developments. Although broadly directed at intermetallic compounds, the discussion is specific to Ni3Al. The hope is that the knowledge and understanding gained about this compound will benefit the class as a whole.

Effect of Hydrogen Content on Structure and Properties of Sintering Body Utilizing TC21 Hydrogenated Powder

2012 ◽  
Vol 581-582 ◽  
pp. 777-781
Author(s):  
Ya Qiang Tian ◽  
Ying Li Wei ◽  
Hong Liang Hou ◽  
Xue Ping Ren
Keyword(s):  
Mechanical Property ◽  
Grain Size ◽  
Titanium Alloy ◽  
Yield Strength ◽  
Hydrogen Content ◽  
Room Temperature ◽  
Sintered Body ◽  
Compressive Yield Strength ◽  
Structure And Properties ◽  
Die Forming

The effect of hydrogenation on structure and properties of TC21 alloy by die forming and sintering using hydrogenated powder was researched by means of the room-temperature die forming and sintering in protection air to produce titanium alloy. The results show that the structure of TC21 titanium sintered body using hydrogenated powder with hydrogen content of 0.39 wt% by die forming and sintering is thinner and the density is higher than the others. The compression strength and compressive yield strength of TC21 sintered body with hydrogen content of 0.39 wt% are well. With hydrogen content increasing, the structure of TC21 production using hydrogenated powder by die forming and sintering gets well and the grain size becomes smaller. After annealing, the structure of TC21 titanium production gets more uniformity and refinement obviously, and the hydrogen content of TC21 alloy safety state is achieved. In the end, the density and mechanical property of TC21 titanium alloy sintered body with hydrogen content of 0.39wt % is the best.

Crack Dynamics and Grain Size

1994 ◽  
Vol 362 ◽  
Author(s):  
John J. Gilman
Keyword(s):  
Grain Size ◽  
Kinetic Energy ◽  
Sound Speed ◽  
Maximum Stress ◽  
Size Dependence ◽  
Terminal Velocity ◽  
Moving Crack ◽  
Fine Grained ◽  
Crack Dynamics ◽  
Relative Kinetic

AbstractTwo aspects of fast cracks are considered: 1. the terminal velocity, and corresponding relative kinetic energy; 2. the grain size dependence of the fracture. It is argued that this is determined by the kinetic energies of cracks when they have expanded enough to reach the boundaries of the grains in which they lie. This is more consistent with the observed facts than the more usual quasi-static models.By considering the limiting conditions at the very tip of a moving crack, many complications are avoided in calculating the terminal velocity. The maximum transverse acceleration of material is limited by the maximum stress (cohesive) that can be applied. The resulting terminal velocity is: 0.4 vs, where vs is the longitudinal sound speed; compared with measured values which average about: 0.31 vs.In polycrystals, microcracks are found when the applied stress exceeds the yield stress. However, the microcracks do not propagate in fine-grained specimens because they do not have enough kinetic energy to cross a typical grain boundary. This leads to the observed dependence of the fracture stress on the grain size.

Colloidal processing and mechanical properties of silicon carbide with alumina

1997 ◽  
Vol 12 (11) ◽  
pp. 3146-3157 ◽  
Author(s):  
Yoshihiro Hirata ◽  
Kouji Hidaka ◽  
Hiroaki Matsumura ◽  
Yasuo Fukushige ◽  
Soichiro Sameshima
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Room Temperature ◽  
Size Dependence ◽  
Theoretical Density ◽  
Aspect Ratios ◽  
Median Size ◽  
Average Grain Size ◽  
Sintering Mechanisms ◽  
Ph Range

Submicrometer-sized SiC coated with SiO2 of 0.4–1.8 wt.% and α–Al2O3 powder of median size 0.2 μm were mixed in aqueous solutions in the pH range 3.0–10.0. The SiC/Al2O3 (4.3–6.9 wt. %) powders were consolidated by filtration through gypsum molds and hot-pressed at 1600°–2040 °C under a pressure of 39 MPa. These compacts were densified to near the theoretical density at 1700°–1800 °C. The sintering mechanisms are discussed based on the analysis of shrinkage curves of SiC/Al2O3 compacts during hot-pressing. The equiaxed SiC grains grew with low aspect ratios below 1800 °C and changed to plate-like grains at 1900 °C. The fracture toughness of SiC as a function of average grain size reached a maximum of 5 Mpa · m0.5 at 2.5 μm grains of low aspect ratios of 1–2. The flexural strengths at room temperature were 230–430 MPa in the SiC above 98% of the theoretical density and showed a similar grain size dependence.

scholarly journals Tensile Strength and Creep Resistance in Nanocrystalline Cu, Pd and Ag

1990 ◽  
Vol 206 ◽  
Author(s):  
G. W. Nieman ◽  
J. R. Weertman ◽  
R. W. Siegel
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Tensile Strength ◽  
Yield Strength ◽  
Creep Resistance ◽  
Room Temperature ◽  
True Strain ◽  
Constant Load ◽  
Creep Tests ◽  
Grain Sizes

ABSTRACTMeasurements of tensile strength and creep resistance have been made on bulk samples of nanocrystalline Cu, Pd and Ag consolidated from powders by cold compaction. Samples of Cu-Cu2O have also been tested. Yield strength for samples with mean grain sizes of 5–80 nm and bulk densities on the order of 95% of theoretical density are increased 2–5 times over that measured in pure, annealed samples of the same composition with micrometer grain sizes. Ductility in the nanocrystalline Cu has exceeded 6% true strain, however, nanocrystalline Pd samples were much less ductile. Constant load creep tests performed at room temperature at stresses of >100 MPa indicate logarithmic creep. The mechanical properties results are interpreted to be due to grain size-related strengthening and processing flaw-related weakening.

Microstructure and mechanical behavior of cast Ti-6Al-4V with addition of boron

2012 ◽  
Vol 2 (3) ◽  
Author(s):  
Robert Pederson ◽  
Raghuveer Gaddam ◽  
Marta-Lena Antti
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Room Temperature ◽  
Compressive Yield Strength ◽  
Strain Rates ◽  
Beta Transus ◽  
Microstructural Refinement ◽  
Compression Properties ◽  
Transus Temperature ◽  
Cast Microstructure

AbstractThe effect of boron (between 0.06 and 0.11 wt%) on the microstructure, hardness and compression properties of cast Ti-6Al-4V was investigated. Compression properties were examined in the temperature range from room temperature to 1000°C. It was found that the addition of boron refines the as-cast microstructure in terms of prior beta grain size and alpha colony size. This microstructural refinement led to an increase in compressive yield strength from room temperature up to 700°C. Three different strain rates (0.001, 0.1 and 1 s−1) were evaluated during compression testing from which it was found that the compressive yield strength decreased with decreasing strain rate from 600°C up to the beta transus temperature.

scholarly journals Nanoindentation-Induced Pile-Up in the Residual Impression of Crystalline Cu with Different Grain Size

2017 ◽  
Author(s):  
Jiangjiang Hu ◽  
Weiming Sun ◽  
Taihua Zhang ◽  
Yusheng Zhang
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Room Temperature ◽  
Indentation Depth ◽  
Dislocation Motion ◽  
Coarse Grained ◽  
Ultrafine Grained ◽  
Pile Up ◽  
Different Grain Size ◽  
Multiple Slips

At room temperature, the indentation morphologies of crystalline copper with different grain size including nanocrystalline (NC), ultrafine-grained (UFG) and coarse-grained (CG) copper were studied by nanoindentation at the strain rate of 0.04/s without holding time at indentation depth of 2000 nm. As the grain size increasing, the height of the pile-up around the residual indentation increases and then has a slightly decrease in the CG Cu, While the area of the pile-up increases constantly. Our analysis has revealed that the dislocation motion and GB activities in the NC Cu, some cross- and multiple-slips dislocation insides the larger grain in the UFG Cu, and forest dislocations from the intragranular Frank-Read sources in the CG Cu, would directly induce these distinct pile-up effect.

Effect of hafnium addition on a Ni-Al-Co Alloy

1990 ◽  
Vol 48 (4) ◽  
pp. 940-941
Author(s):  
L. S. Lin ◽  
G. W. Levan ◽  
S. M. Russell ◽  
C. C. Law
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Yield Strength ◽  
Grain Boundaries ◽  
Ternary Alloy ◽  
Room Temperature ◽  
Gamma Prime ◽  
Room Temperature Ductility ◽  
Appreciable Increase ◽  
Hf Addition

Recent efforts at P&W have shown that the addition of cobalt to binary NiAl results in an appreciable increase in room temperature ductility. One version of this ternary alloy, designated VIM A, has a composition of Ni-30 at.% Al-35 at.% Co. The addition of 0.5 at.% Hf to this alloy (designated VIM AH) results in an improvement in yield strength at 760°C. Room temperature properties were not found to be significantly affected by the Hf addition. This discussion will focus on the microstructures of alloys VIM A and VIM AH and their relationship to the mechanical properties observed in compression at room temperature and 760°C.The addition of hafnium reduced the grain size of VIM AH alloy. After room temperature compression, both alloys show an ordered bcc (B2) matrix and precipitates which are distributed primarily along grain boundaries. These precipitates were identified by microdiffraction to be ordered fcc (L12) gamma prime for VIM A and hexagonal (A3) for VIM AH.

SIZE EFFECT OF FLOW STRESS IN ISOTHERMAL UPSETTING DEFORMATION

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1745-1750
Author(s):  
BIN GUO ◽  
CHUNJU WANG ◽  
DEBIN SHAN ◽  
LINING SUN
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Size Effect ◽  
Room Temperature ◽  
Size Dependence ◽  
Treatment Process ◽  
Different Dimensions ◽  
Single Grain ◽  
The Difference ◽  
Different Grain Size

With the miniaturization of parts, size effect occurs. The isothermal forming processes are performed to obtain homogenizing deformation. In the paper, a serial of isothermal upsetting tests are carried out with billets of different dimensions. Difference of flow stress is accepted as the parameter to evaluate the size dependence of flow stress on billets dimensions. The experimental results show that size effect occurs clearly. With the increasing of temperature, the difference of flow stress becomes smaller, which means that the degree of size dependence is reduced. Scatter of flow stress is observed in the tests at room temperature. When the deformation temperature is raised, the fluctuation of flow stress tends towards decreasing. In order to investigate the effect of grain size, different grain size is obtained with the heat treatment process. At the same temperature, the difference of flow stress increases with the increasing of grain size. These phenomena can be explained from the viewpoint of polycrystalline structure of material. The anisotropy of individual grain is appeared obviously, which leads the fluctuation of flow stress. In the isothermal deformation, the effect of single grain is smaller than that at room temperature.

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