A Creep Model for Solder Alloys

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Yongchang Lee ◽  
Cemal Basaran
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Diffusion Processes ◽  
Dislocation Motion ◽  
Creep Model ◽  
Solder Alloys ◽  
Creep Models ◽  
And Diffusion ◽  
Cycling Loading

Demand for long-term reliability of electronic packaging has lead to a large number of studies on viscoplastic behavior of solder alloys. Various creep models for solder alloys have been proposed. They range from purely empirical to mechanism based models where dislocation motion and diffusion processes are taken into account. In this study, most commonly used creep models are compared with the test data and implemented in ABAQUS to compare their performance in cycling loading. Finally, a new creep model is proposed that combines best features of many models. It is also shown that, while two creep models may describe the same material stress–strain rate curves equally well, they may yield very different results when utilized for cycling loading. One interesting observation of this study is that the stress exponent, n., also depends on the grain size.

A Viscoplasticity Model for Solder Alloys

2010 ◽  
Author(s):  
Yongchang Lee ◽  
Cemal Basaran
Keyword(s):  
Grain Size ◽  
Diffusion Processes ◽  
Dislocation Motion ◽  
Creep Model ◽  
Plastic Behavior ◽  
Solder Alloys ◽  
Creep Models ◽  
And Diffusion ◽  
Cycling Loading

Demand for long-term reliability of electronic packaging has lead to a large number of studies on visco-plastic behavior of solder alloys. Various creep models for solder alloys have been proposed. They range from purely empirical to mechanism based models where dislocation motion and diffusion processes are taken into account. In this study, most commonly used creep models are compared with the test data and implemented in ABAQUS to compare their performance in cycling loading. Finally, a new creep model is proposed that combines best features of many models. It is also shown that, while two viscoplasticity models may describe the same material stress-strain rate curves equally well, however they may yield very different results when utilized for cycling loading. One interesting observation of this study is that the stress exponent, n, also depends on the grain size.

Effect of Long-Term Aging on the Tensile Properties of Nickel-Based Superalloy

2012 ◽  
Vol 430-432 ◽  
pp. 7-11 ◽  
Author(s):  
Li Wei Xu ◽  
Hua Bing Li ◽  
Qi Feng Ma ◽  
Zhou Hua Jiang
Keyword(s):  
Strain Rate ◽  
Tensile Properties ◽  
Aging Time ◽  
High Strain ◽  
Dislocation Motion ◽  
Strengthening Phase ◽  
Obvious Effect ◽  
Nickel Based Superalloy ◽  
Coordination Ability

The influence of microstructure evolution of a nickel-based superalloy after long-term aging on the tensile properties and deformation behavior was investigated. The results shows that the aging time exhibits an significant effect on the strength of alloy under low strain rate and the elongation decrease with increasing the aging time, but the aging time has no obvious effect on the strength of the alloy and elongation is affected significantly by aging time. During deformation under high strain rate, the dislocation motion is blocked and the dislocation can not release in time, the strengthening phase peak size effect does not appear in the aging time ranging from 0h to 1000h, so the influent of aging time on the strength of the alloy is not obvious. After long-term aging, no precipitation appear in both sides of the grain boundary which leads to the coordination ability of plastic deformation of grain boundaries reducing, so the ductility of the alloy decreases rapidly in a short aging time.

What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?

2006 ◽  
Vol 976 ◽  
Author(s):  
Christopher Carlton ◽  
P. J. Ferreira
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Critical Value ◽  
Petch Relationship ◽  
And Diffusion ◽  
Critical Grain Size

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.

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.

Deformation Characteristics and Constitutive Relationship of SnAgCu Lead (Pb)-Free Solder Alloys Under Thermo-Mechanical and Mechanical Loading

2006 ◽  
Author(s):  
Mohammad M. Hossain ◽  
Puligandla Viswanadham ◽  
Dereje Agonafer ◽  
Tommi Reinikainen
Keyword(s):  
Solder Joint ◽  
Strain Rate ◽  
Coefficient Of Thermal Expansion ◽  
Bulk Solder ◽  
Constitutive Relationship ◽  
Lead Free ◽  
Creep Model ◽  
Solder Alloys ◽  
Lap Shear ◽  
Constitutive Parameters

In this paper is reported the mechanical and thermomechanical aspect of SnAgCu solder alloys that have been tested for their deformation behavior. Commercially available Sn3.8Ag0.7Cu was considered as base alloy. The constant stress and strain-rate tests were performed in tensile and shear configuration. Mechanical deformations were measured using bulk solder tensile specimens and grooved lap shear specimens which enabled a stress-state of nearly pure shear in the solder joint. The strain rate range was between 0.1/sec and 10-6/sec, and test temperatures were 25°C, 75°C and 125°C. Both as-prepared and thermally aged samples were tested. The aging condition was 24hrs at 125°C. The measured tensile stress-strain data were utilized to determine the constants for the visco-plastic Anand's constitutive model. Thermo-mechanical properties like coefficient of thermal expansion (CTE) for those SnAgCu lead free alloys were measured in the temperature range of - 40 to 160°C using thermo-mechanical analyzer (TMA). The tensile and shear properties of 95.5Sn3.8Ag0.7Cu solder and solder joint specimens are highly dependent on test temperature and strain rate. The mechanical strength of SAC bulk solder and solder joint decreases with increase in temperature and increases with increase in strain rate. CTE for the SAC lead-free alloys were relatively lower compared with tin-lead solder. The steady-state creep test data for 95.53.8Ag0.7Cu solder was curve-fitted to a hyperbolic-sine creep model. The material constitutive parameters developed are in line with similar studies.

scholarly journals Role of Grain Size and Shape in Superplasticity of Metals

2021 ◽  
Vol 8 ◽  
Author(s):  
Zhaoyang Lu ◽  
Xuqiang Huang ◽  
Jingzhe Huang
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Diffusion Processes ◽  
Energy Requirement ◽  
Rate Sensitivity ◽  
Superplastic Forming ◽  
Testing Temperature ◽  
Ferrous Alloys ◽  
Size And Shape ◽  
Grain Size And Shape

Superplasticity is characterized by an elongation to failure of >300% and a measured strain rate sensitivity (SRS), close to 0.5. The superplastic flow is controlled by diffusion processes; it requires the testing temperature of 0.5Tm or greater where Tm is the absolute melting temperature of metals. It is well established that a reduction in grain size improves the optimum superplastic response by lowering the deformation temperature and/or raising the strain rate. The low-temperature superplasticity (LTSP) is attractive for commercial superplastic forming, in view of lowering energy requirement, increasing life for conventional or cheaper forming dies, improving the surface quality of structural components, inhibiting quick grain growth and solute-loss from the surface layers, thus resulting in better post-forming mechanical properties. This paper will summarize the dependence of superplasticity on grain size and shape in various metallic materials, including ferrous and non-ferrous alloys, which has been considered as an effective strategy to enable the LTSP.

Understanding the microscopic deformation mechanism and macroscopic mechanical behavior of nanocrystalline Ni by the long-term stress relaxation test

2014 ◽  
Vol 28 (20) ◽  
pp. 1450124 ◽  
Author(s):  
Xixun Shen ◽  
Congcong Zhang ◽  
Tao Zeng ◽  
Danhong Cheng ◽  
Jianshe Lian
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Mechanical Behavior ◽  
Deformation Mechanism ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Relaxation Behavior ◽  
Nonlinear Stress ◽  
Two Stages

The long-term stress relaxation tests with a relaxation time of about 7 h are performed on the bulk dense nanocrystalline Ni (with a mean grain size of 27 nm) pre-deformed at strain rate from 4.17 s-1- 4.17 × 10-6 s-1, where a phenomenon that the initial relaxation behavior of nc Ni depends on itself deformation history. That is, the nc Ni s pre-deformed at higher strain rate (not less than 4.17 × 10-3 s-1) exhibit a three-staged relaxation process from the initial near linear rapidly stress delayed (LRSD) stage and the subsequent lumber nonlinear stress delayed (LNSD) one and the final near linear slowly stress delayed (LSSD) one while only the later two stages are observed for the nc Ni s pre-deformed at low strain rate. The three-stage relaxation behavior is attributed to the transition from the initial dislocation-dominated plasticity to the mixture of dislocation motion and diffusion-based GB activity and finally to the entire diffusion-based GB activity including GB sliding or grain rotation in the rate-controlling deformation mechanism, which was illuminated by the attained three-staged strain rate sensitivity and activation volume and the exhaustion of mobile density of deformed nc Ni in the first two stages of relaxation. Such rate-controlling deformation mechanism well interpreted the macroscopic tensile mechanical behavior of nc Ni and simultaneously an optimizing strategy in improving the ductility of nc Ni is also mentioned.

Effect of Natural Aging on RT and HSR Superplasticity of Ultrafine Grained Zn-22Al Alloy

2016 ◽  
Vol 838-839 ◽  
pp. 320-325 ◽  
Author(s):  
Muhammet Demirtas ◽  
Gencaga Purcek ◽  
Harun Yanar ◽  
Zhen Jun Zhang ◽  
Zhe Feng Zhang
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Equal Channel Angular Extrusion ◽  
Natural Aging ◽  
Maximum Elongation ◽  
Microstructural Stability ◽  
Grain Sizes ◽  
Ultrafine Grained ◽  
Lower Strain

Zn–22Al alloy was processed using a well-designed two-step equal channel angular extrusion/pressing (ECAE/P), and ultrafine-grained (UFG) microstructure with 200 nm grain size was achieved. UFG Zn-22Al was subjected to long-term (up to 60 days) aging at room temperature (RT) and it was seen that natural aging caused limited grain growth in the microstructure. Grain sizes of about 300 nm, 350 nm and 350 nm were measured after 15, 30 and 60 days aging, which mean that UFG Zn-22Al alloy has a good microstructural stability at RT up to 60 days. ECAPed Zn-22Al alloy showed a maximum elongation of about 400% at a high strain rate of 5x10-2 s-1 and maximum elongation decreased with increasing grain size. Elongation to failures of ~375% and ~350% were obtained with the samples having 300 nm and 350 nm grain sizes, respectively. In addition, natural aging slightly decreased the strain rate at which superplastic region formed. While the maximum elongation occurred at the strain rate of 5x10-2 s-1 in ECAPed UFG alloy, it took place at lower strain rate of 1x10-2 s-1 after aging for all time periods. Also, flow stress of the alloy increased with increasing grain size during natural aging.

Meridional Circulation, Turbulence, and Diffusion Processes in Stars

1976 ◽  
Vol 32 ◽  
pp. 109-116 ◽  
Author(s):  
S. Vauclair
Keyword(s):  
Convection Zone ◽  
Diffusion Processes ◽  
Meridional Circulation ◽  
Diffusion Time ◽  
Work In Progress ◽  
First Results ◽  
Stellar Envelopes ◽  
And Diffusion ◽  
Turbulence And Diffusion ◽  
Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

NMR-Study of Structure and Diffusion Processes in Li3N

1980 ◽  
Vol 41 (C6) ◽  
pp. C6-28-C6-31 ◽  
Author(s):  
R. Messer ◽  
H. Birli ◽  
K. Differt
Keyword(s):  
Diffusion Processes ◽  
Nmr Study ◽  
And Diffusion
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