Effects of Microstructures on the Mechanical Properties of Dilute Al-Si Alloys

2007 ◽  
Vol 345-346 ◽  
pp. 821-824
Author(s):  
Keiyu Nakagawa ◽  
Teruto Kanadani
Keyword(s):  
Fatigue Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Aging Time ◽  
Fracture Elongation ◽  
Micro Cracks ◽  
Hand Fracture ◽  
Stress Cycles ◽  
Effects Of Aging ◽  
The Relationship

In this paper, we investigated effects of aging at 473K on the relationship between microstructure in the vicinity of the grain boundaries and fatigue strength for Al-1.2%Si alloy. Results obtained show the following features. (1) As aging time, tA increase, the tensile strength (σB) and 0.2% proof stress (σ0.2) increase slowly, but gradually decrease after reaching a maximum at around 18 ks. On the other hand, fracture elongation shows an opposite trend, suggesting that at aging times above 18ks, over aging occurs. (2) The fatigue strength lowers with increasing aging time, however, when the aging time is more than 18 ks at 473K, the fatigue strength remains almost the same. (3) When the aging time is more than 6 ks, grain boundary precipitates with a size greater than several 10s of nm are observed. (4) When the aging time is 18 ks, an accumulation of dislocations are observed at the grain boundaries and in the vicinity of grain boundary precipitates, and dislocations increase with the number of stress cycles. (5) When the aging time is more than 6 ks, the fatigue fracture surface is mainly intergranular. These results suggest that reduction of fatigue strength results from propagation of micro-cracks which are initiated at the large precipitates on the grain boundaries.

Study of Bonding of Grain Boundaries in Steels Using EELS

2005 ◽  
Vol 475-479 ◽  
pp. 4063-4066
Author(s):  
X. Zhang ◽  
Lina Zhang ◽  
Jun Jie Qi ◽  
Yue Ma
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Fracture ◽  
Fracture Mode ◽  
Fracture Property ◽  
Transgranular Fracture ◽  
The Difference ◽  
Relationship Of ◽  
The Relationship

A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.

Evolution of Precipitate Depleted Zones in Mg-Based Alloys Strengthened by Precipitation Hardening

2009 ◽  
Vol 289-292 ◽  
pp. 153-159
Author(s):  
A. Katsman ◽  
Anton Gorny ◽  
D. Shepelev ◽  
Menachem Bamberger
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Aging Time ◽  
Precipitation Hardening ◽  
Research Work ◽  
Interface Energy ◽  
Physical Parameters ◽  
Model Parameters ◽  
Different Temperatures ◽  
Outer Border

Extensive research work has been devoted to Mg-based alloys strengthened by precipitation hardening. Increasing the aging time leads to the appearance of zones depleted of precipitates near grain boundaries. The formation of precipitate depleted zones (PDZ's) is explained by near-grain boundary (NGB) coarsening. The evolution of PDZ's was considered on the basis of the model taking into account diffusional fluxes between adjacent precipitates. The set of equations was solved numerically by using a fourth-order Runge-Kutta method for different initial sizes of precipitates and densities of precipitate layers near grain boundaries. The dissolution of precipitates in the NGB-zones is initially provided by diffusion from them to large precipitates at the grain boundary, and then also by diffusion from these decreased precipitates to the larger precipitates at the outer border of the PDZ. As a result, the outer borders of the depleted zones are adjoined by bands of enlarged precipitates forming a PDZ "crust". Being a diffusion controlled process, the depleted zones are widened with temperature and aging time. Experimental investigation of PDZ evolution was conducted by SEM and TEM on Mg-Zn-Sn-alloys aged at different temperatures for different times. Comparison of the calculated results with experimental data allowed the evaluation of the model parameters and physical parameters of the system (diffusion coefficients and interface energy of the precipitated phases).

Morphology Evolution of Grain Boundary Carbides in Highly Twinned Inconel Alloy 600

2016 ◽  
Vol 879 ◽  
pp. 1111-1116 ◽  
Author(s):  
Hui Li ◽  
Jiao Rong Ma ◽  
Xin Rong Liu ◽  
Shuang Xia ◽  
Wen Qing Liu ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Aging Time ◽  
Electron Backscatter Diffraction ◽  
Coincidence Site Lattice ◽  
Morphology Evolution ◽  
Alloy 600 ◽  
Inconel Alloy ◽  
Electron Backscatter ◽  
Backscatter Diffraction

The effects of grain boundary characters on the morphology evolution of grain boundary carbides in Inconel Alloy 600 with high proportional low Σ coincidence site lattice (CSL) boundaries aged at 715 oC for 1-100 h were investigated by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). During the aging process, the carbides precipitated at coherent twin (Σ3) boundaries are very few and finest within all the aging time. Bar like carbides precipitated near both sides of the incoherent twin (Σ3) boundaries, and bigger carbides than that of coherent Σ3 boundaries had been found on the incoherent Σ3 boundaries. Bar like carbides precipitated near only one side of Σ9 boundaries, and much bigger carbides than that of Σ3 boundaries have been found on the Σ9 boundaries. The morphology of carbides precipitated at Σ27 and random grain boundaries are similar, and is bigger than that of precipitated at other grain boundaries. The carbides precipitated at grain boundaries with all types grow bigger with the aging time prolonging, but their growth rates are different.

scholarly journals Molecular dynamics investigation on tilt grain boundary energies of beta-titanium and tungsten at high temperature

2021 ◽  
Author(s):  
Hong He ◽  
Shangyi Ma ◽  
Shaoqing Wang
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Dynamic Simulations ◽  
Beta Titanium ◽  
Symmetric Tilt ◽  
Higher Temperature ◽  
Lattice Misorientation ◽  
The Relationship ◽  
Variation Trends

Abstract The grain boundary energies (GBEs) of symmetric tilt grain boundaries (STGBs) and asymmetric tilt grain boundaries (ATGBs) for W at 0 and 2400 K and β-Ti at 1300 K were calculated by means of Molecular static method and Molecular dynamic simulations to investigate the effects of high temperature and grain boundary (GB) planes on the GBE. Generally, the variation trends of GBEs functioned with tilt angle are similar in the three cases when the tilt axis is specified. It is of course that these similarities result from their similar GB microstructures in most cases. However, the variation trends of β-Ti at 1300 K are somewhat different from that of W at 2400 K for STGBs with <100> and <110> tilt axes. This difference mainly stems from the following two reasons: firstly, the GB microstructures of W at 2400 K and β-Ti at 1300 K are different for some STGBs; secondly, the atoms at STGB of β-Ti at 1300 K tend to evolve into the local ω- or α-like structures distributed at STGBs, which make the corresponding STGBs more stable, thereby decreasing the GBEs. Furthermore, a geometric parameter θ, an angle between misorientation axis and GB plane, was defined to explore the effects of GB planes on GBEs. It was found that the relationship between GBEs and sin(θ) can be described by some simple functions of sin(θ) for the GBs with definite lattice misorientation, which can well explain and predict the preferred GB planes for the GBs with specific lattice misorientation. Our calculations not only extend the investigation of GBs to higher temperature, but also deepen the understanding on the temperature contribution to the microstructure evolution at GBs and on the relationship between GBE and possible geometric parameters.

Morphological Changes in Rod-Shaped Precipitates With Internal Boundaries: Finite Difference Analysis

1991 ◽  
Vol 237 ◽  
Author(s):  
Jun-Ho Choy ◽  
S. A. Hackney ◽  
J. K. Lee
Keyword(s):  
Aspect Ratio ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Morphological Changes ◽  
Equilibrium Shape ◽  
Interfacial Free Energy ◽  
Dynamic State ◽  
Shape Evolution ◽  
Boundary Groove ◽  
The Relationship

ABSTRACTShape evolution of rod-shaped precipitates due to surface diffusion has been studied under the conditions of constant volume and isotropie interfacial free energy. The shape evolution depends strongly on both the initial aspect ratio and the grain boundary groove angle. For a finite rod with one grain boundary, the morphology evolves into an equilibrium shape made of spherical portions if its aspect ratio and the groove angle are small. Increase in the aspect ratio causes a boundary splitting. For an infinite rod with periodic boundaries, three types of morphological evolutions are observed. When the relationship between the aspect ratio and the groove angle satisfies a certain critical condition, the shape evolves into an equilibrium. If the relationship deviates significantly from this condition, an ovulation process takes place at each location of the internal grain boundaries. When the deviation is intermediate, the morphology undergoes an oscillation in a quasi-dynamic state between the process toward an equilibrium shape and the ovulation process. The ovulation process due to internal grain boundaries is found to precede the Rayleigh spheroidization process.

Microcracking in Polycrystalline Solids

1988 ◽  
Vol 110 (2) ◽  
pp. 101-104 ◽  
Author(s):  
N. Laws ◽  
J. R. Brockenbrough
Keyword(s):  
Grain Boundary ◽  
Residual Stresses ◽  
Grain Boundaries ◽  
Applied Load ◽  
Process Zone ◽  
Crack Density ◽  
Hexagonal Array ◽  
Brittle Solid ◽  
Micro Cracks ◽  
Polycrystalline Solids

A polycrystalline brittle solid may undergo grain boundary micro-cracking due to residual stresses or applied load. This paper contains some results pertaining to the loss of macroscopic stiffness of such solids when all micro-cracks are open and when some may be closed and be subject to frictional sliding. Two specific models are investigated: first micro-cracking on the grain boundaries of a regular hexagonal array, second, micro-cracks which are randomly located and oriented. It is shown that for many purposes the two models give identical results. The paper concludes with some analysis of the possible toughening due to process zone micro-cracking at the tip of a macroscopic crack. It is found that toughening can only occur if the saturation crack density is very large.

Effects Of Cation Segregation At Oxide Grain Boundaries On Grain Boundary Diffusion And Oxidation Kinetics Of Nickel

1991 ◽  
Vol 238 ◽  
Author(s):  
C. M. Cotelia ◽  
M. J. Bennett ◽  
A. J. Garratt-Reed
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Oxidation Mechanism ◽  
Grain Boundary Segregation ◽  
Reactive Element ◽  
Protective Oxide ◽  
General Applicability ◽  
The Relationship ◽  
Kinetics Of

ABSTRACTThe oxidation behavior of Ni, implanted with either divalent Ce2+ or trivalent Y3+, has been studied to test the general applicability of the grain boundary segregation explanation for the reduction in rate of oxidation resulting from reactive element additions to metals that form protective oxide scales. Oxidation of Ce- and Y-implanted Ni at 900°C resulted in grain boundary segregation of the implanted species in the NiO scales formed. The rate of oxidation of Ni was reduced and there was evidence for a change in oxidation mechanism. Additionally, the grain size of the oxides was much smaller. All the observations were entirely consistent with a reduction in cation transport resulting from segregation of foreign ions at the oxide grain boundaries. These results on Ni are compared with recent studies of Ce- and Y-implanted Cr to draw general conclusions about the relationship between grain boundary segregation in oxides and the reactive element effect on oxidation.

Effect of prestrain on microstructure and mechanical behavior of aged Ti–10V–2Fe–3Al alloy

2009 ◽  
Vol 24 (9) ◽  
pp. 2899-2908 ◽  
Author(s):  
Wei Chen ◽  
Zhenya Song ◽  
Lin Xiao ◽  
Qiaoyan Sun ◽  
Jun Sun ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Tensile Strength ◽  
Grain Boundary ◽  
Mechanical Behavior ◽  
Grain Boundaries ◽  
Aging Time ◽  
Transmission Electron ◽  
Α Particles

The effect of prestrain on microstructure and mechanical behavior of aged Ti–10V–2Fe–3Al alloy was investigated. The results showed that prestrain caused the tensile strength to decrease by 5%, but the elongation to fracture significantly improved by about 200%, in comparison with the unstrained samples, using a much shorter aging time. Transmission electron microscopy investigations showed that nano-sized alpha (α) particles homogeneously precipitated in the beta (β) matrix, and continuous α films formed along grain boundaries in the unstrained and aged samples. However, in the prestrained samples, the coarse stress induced martensite laths decomposed into α- and β-phases in the form of alternately arranged plates, which suppressed formation of the continuous grain boundary α films during aging. The hardness of the prestrained samples was lower than that of the unstrained samples after the same aging treatments. The enhancement of ductility can be mainly attributed to the suppression of grain boundary α films and the reduced hardness in prestrained samples.

Fatigue Damage Mechanism of Titanium in Inert Environments

2012 ◽  
Vol 225 ◽  
pp. 225-229
Author(s):  
Nur Ismarrubie Zahari ◽  
H. Yussof ◽  
M. Sugano
Keyword(s):  
Fatigue Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Fatigue Damage ◽  
Thin Plate ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Damage Mechanism ◽  
Lattice Defects ◽  
Argon Gas

The fatigue damage of titanium has been studied on thin plate specimens subjected to alternating plane bending in argon gas. Fatigue strength in argon gas at Nf = 108 cycles was obtained to be 102 MPa. Fatigue behavior of titanium in argon gas has been attributed to the degradation of grain boundary cohesion with argon gas atoms/molecules. Fatigue cracks were propagated partly in intergranular mode. It has been plausible that argon gas atoms/molecules could penetrate into the distorted regions close to grain boundary through lattice defects and degrade grain boundary cohesion. Grain boundaries have been preferentially damaged in argon gas. The results in argon gas have been compared with those obtained in vacuum and in air.

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