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).

Effect of Precipitate Depleted Zones on Precipitation Hardening in Mg-based Alloys

2008 ◽  
Vol 1128 ◽  
Author(s):  
D. Shepelev ◽  
A. Katsman ◽  
E. Edelshtein ◽  
M. Bamberger
Keyword(s):  
Experimental Investigation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Precipitation Hardening ◽  
Boundary Zone ◽  
Corrosion Properties ◽  
The Matrix ◽  
Different Temperatures ◽  
Large Round ◽  
Mechanical And Corrosion Properties

AbstractThe formation of precipitate depleted zones (PDZ) near grain boundaries in Mg-based alloys strengthened by precipitation hardening is deemed as detrimental to the material since wide depleted zones may affect the mechanical and corrosion properties of the alloy. Experimental investigation of PDZ evolution in Mg-Zn-Sn-alloys aged at different temperatures for different times was conducted by SEM and TEM and by measuring the microhardness of near grain boundary zones at low loads. It was found that at early stages of aging (175°C, ≤1 day) the hardening is caused by formation of MgZn2 needle- and T-like MgZn2/Mg2Sn particles. The neargrain boundary zone is harder than the grain matrix, due to large round MgZn2 and Mg2Sn particles formed at grain boundaries. Increasing the aging was found to decrease the hardening in the matrix as well as in the near-grain boundary zones due to the dissolution of MgZn2 needles and the coarsening of T-like particles. Substantial microhardness decrease in the near-grain boundary zone (from 70 to ~30 HV) found at low loads (10 gr) was connected with the formation of PDZ. This was confirmed by TEM and SEM studies. Further aging, at 225°C for 1-8 days, leads to the formation of "crusts" of enlarged T-like particles around depletion zones. As a result, the microhardness of PDZ's measured at higher loads (25 and 50 gr) increases up to ~ 60÷70 HV close to the ones measured in the grain matrix.

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.

Stabilization of Microstructures in Mg-Based Alloys: Modeling and Processing

2010 ◽  
Vol 95 ◽  
pp. 51-54
Author(s):  
A. Katsman ◽  
Menachem Bamberger
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Structural Stability ◽  
Phase Formation ◽  
Precipitation Hardening ◽  
Elevated Temperatures ◽  
Research Work ◽  
Boundary Structure ◽  
Promising Candidate ◽  
Grain Boundary Structure

Extensive research work was devoted to Mg-based alloys strengthened by precipitation hardening. In this framework, the Mg-Zn-Sn system was considered a promising candidate for a creep resistant Mg-alloy. Small additions of alloying elements forming high temperature phases (HTP) were used to improve the structural stability of the Mg-Zn-Sn alloy. Phase formation during solidification was analyzed using thermodynamic calculations. The influence of HTP-particles on stabilization of sub-grain boundary structure was found to be of great importance in improving structural stability of the alloys at elevated temperatures. Mechanisms of precipitation hardening were investigated using the modified Langer-Schwartz model calibrated for Mg-Zn-Sn alloys.

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.

Influence of the grain boundaries on conductivity of yttrium stabilized zirconia

2004 ◽  
Vol 835 ◽  
Author(s):  
V. Petrovsky ◽  
P. Jasinski ◽  
H.U. Anderson ◽  
T. Petrovsky
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Tape Casting ◽  
Casting Process ◽  
Boundary Resistance ◽  
Unit Surface Area ◽  
Stabilized Zirconia ◽  
Different Temperatures ◽  
Overall Resistance

ABSTRACTThe influence of the grain boundaries on the ionic conductivity of yttrium stabilized zirconia (YSZ) was investigated. The initially nanocrystalline samples were prepared using a tape casting process. The samples were annealed at different temperatures in the range from 1000 to 1400°C to overlap the grain size from 100nm to ∼10μm and investigated using impedance spectroscopy. Two distinct semicircles were found on all YSZ samples corresponding to the influence of the grain and grain boundary on the resistance. The activation energies for both resistances are very close (1.00 and 1.03eV correspondingly). The grain resistance does not change significantly during the annealing process, but the grain boundary resistance decreases after high temperature annealing which causes a decrease in the overall resistance of the material. The calculations show that the decrease in the grain boundary resistance is connected only with the increase in the grain size and the specific grain boundary resistance (per unit surface area of grain boundary) does not change with annealing.

Fuzzy Decentralized Controller Design with Internet of Things for Urban Trains

2020 ◽  
Vol 12 (3) ◽  
pp. 422-433 ◽  
Author(s):  
Seyyed Mohammad Hosseini Rostami ◽  
Vahid Alimohammadi
Keyword(s):  
Internet Of Things ◽  
Dynamic Model ◽  
Pid Controller ◽  
Closed Loop ◽  
Controller Design ◽  
Research Work ◽  
Conversion Function ◽  
Physical Parameters ◽  
Model Parameters ◽  
The Stability

Due to the dynamic structure and physical constraints that exist in controlling the urban train system, the physical parameters of the urban train model are constantly changing, and therefore a static controller cannot fully control all of the control objectives to be defined. In this paper, a new method of using a PID controller based on fuzzy control with considering the uncertainty of the weight of the dynamic model of the system is presented for managing the dynamical model of the urban train. The primary objective of this research work is to provide a structure that simultaneously, in addition to guaranteeing the stability of the Kharitonov polynomials, the dynamic model of the sample system also automatically adjusts and controls the proposed controller control parameters. In order to introduce model uncertainties into the controller design calculations, Kharitonov polynomials related to the open loop conversion function are first extracted. Then the feedback loop is constructed with a parallel PID controller, and by rewriting the closed-loop conversion function equations, we obtain the set of all closed-loop system transformation functions, in which the model's indices are also considered. Subsequently, by examining the stability ranges of all closed-loop functions, the values obtained for the proportional, integral, and derivative parameters of the PID controller are obtained for its robust performance. Finally, a fuzzy-based structure is proposed for intelligent operation and online adjustment of proposed PID controller coefficients. Further, this research work outlines twolevel Internet of Things (IoT) sensor network that compliments the proposed mathematical model by providing real-time model parameters using the sensory information.

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.

scholarly journals Molecular Dynamics Calculations of Grain Boundary Mobility in CdTe

Nanomaterials ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 552 ◽  
Author(s):  
Rodolfo Aguirre ◽  
Sharmin Abdullah ◽  
Xiaowang Zhou ◽  
David Zubia
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Driving Forces ◽  
Md Simulations ◽  
Face Centered Cubic ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Different Temperatures ◽  
Lower Mobility

Molecular dynamics (MD) simulations have been applied to study mobilities of Σ3, Σ7 and Σ11 grain boundaries in CdTe. First, an existing MD approach to drive the motion of grain boundaries in face-centered-cubic and body-centered-cubic crystals was generalized for arbitrary crystals. MD simulations were next performed to calculate grain boundary velocities in CdTe crystals at different temperatures, driving forces, and grain boundary terminations. Here a grain boundary is said to be Te-terminated if its migration encounters sequentially C d · T e − C d · T e … planes, where “·” and “−” represent short and long spacing respectively. Likewise, a grain boundary is said to be Cd-terminated if its migration encounters sequentially T e · C d − T e · C d … planes. Grain boundary mobility laws, suitable for engineering time and length scales, were then obtained by fitting the MD results to Arrhenius equation. These studies indicated that the Σ3 grain boundary has significantly lower mobility than the Σ7 and Σ11 grain boundaries. The Σ7 Te-terminated grain boundary has lower mobility than the Σ7 Cd-terminated grain boundary, and that the Σ11 Cd-terminated grain boundary has lower mobility than the Σ11 Te-terminated grain boundary.

Measurement of the Displacement Across a Coincidence Grain Boundary

1977 ◽  
Vol 35 ◽  
pp. 124-125
Author(s):  
J. W. Matthews ◽  
W. M. Stobbs
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stacking Fault ◽  
The Other ◽  
Measuring Technique ◽  
High Angle ◽  
Twin Boundaries ◽  
Rigid Displacement ◽  
Cubic Crystals ◽  
Lattice Displacement

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

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