Mechanical property and structural changes by thermal cycling in phase-separated metallic glasses

Nondestructive cryogenically thermal cycling has been a simple but effective treatment to enhance mechanical properties of glassy materials.However,how the structural heterogeneities on nanometer scales are affected by thermal cycling is still an issue.Here,we report the response of spatial hetero-geneities in three selected Ti41Zr25Be28Fe6,Zr56Co14Cu14Al16 and Zr42Y14Co22Al22(at.％)metallic glasses(MGs)with different compositions to the thermal cycling,which show significantly different structure and properties after the same treatments and could be ascribed to the joint contribution of relaxation and rejuvenation induced by thermal cycling.The rejuvenation is initially prevailed in a Zr-Y-containing MG,whereas the relaxation is dominant in a Cu-Co-containing MG,both eventually entering into a dynamic equilibrium state.By employing nanometer-scale structural models,the intrinsic correlation between the spatial heterogeneity and thermal cycling is proposed.The discovery could provide the fundamental understanding of the role of spatial heterogeneity in influencing the macroscopic properties of MGs via thermal cycling and help design high-performance glassy materials by tailoring their atomic structures with suitable thermal treatments.     

The coupling effects of thermal cycling and high current density on Sn58Bi solder joints

Currently, one of the serious challenges in microelectronic devices is the miniaturization trend of packaging. As the decrease of joint dimension, electromigration (EM) and thermomechanical fatigue become critical issues for fine pitch packaging. The independent mechanisms of EM and thermomechanical fatigue are widely investigated and understood. However, the coupling effect of both conditions needs further exploration. The current study established the correlation between resistance and microstructure evolution of solder joint under the combination effect of thermal cycling and high current density and illustrated the different contributions of these two factors to the reliability of the joint through the comparison monopoly tests. The results revealed that cracks had more impact on resistance increase than phase segregation. The resistance evolution could be divided into three stages. First, the resistance mitigated due to the phase coarsening. Second, Joule heating effect made the resistance increase slowly. Third, EM led to the resistance increase rapidly. The high current density can help to improve the reliability of the solder joint under the coupling effect of thermal cycling and EM at the initial stage, but harmful to the consequence process.     

Effects of thermal cycling on trinitrotoluene and tritonal explosive compositions

The effects of thermal cycling of Trinitrotoluene (TNT) and tritonal were studied using unprocessed virgin TNT, reclaimed TNT and laboratory prepared tritonal. Small quantities of explosives were temperature cycled through ranges designed to simulate aerodynamic heating. The thermal chemical kinetics at isothermal temperatures were investigated using differential scanning calorimetry methods. Physical and Chemical changes were studied using Scanning Electron Microscopy, X-ray diffraction, and Thin-Layer Chromatography (TLC) techniques.     

Failure during thermal cycling of plasma-sprayed thermal barrier coatings

The thermal cycling behavior of plasma-sprayed ZrO₂?12wt.%Y₂O₃ coatings was studied. Coatings were produced with and without bond coats of Ni-Cr-Al-Zr and in some cases the substrates were heated to above the optimum temperature prior to spraying. The coatings (attached to the substrate) were thermal cycled to 1200 °C and their cracking behavior was followed by acoustic emission (AE) techniques. It was possible to examine the failure mechanisms by statistical analysis of the AE data and to evaluate the influence of preheating and bond coating. It is shown that the AE spectrum changes when a bond coat is used because of the presence of microcracks which, in turn, dissipate energy and improve the coating integrity. The preheating effect is reflected by a decrease in the peak count rate and an increase in the temperature at which AE activity is initiated.     

Immobilization of sodium and potassium in Synroc

Substitution of K for Na in certain nuclear fuel reprocessing cycles may allow an increase of waste loading in Synroc, because K can be incorporated in the barium hollandite phase more easily than Na. The use of rare-earth additions to stabilize Na in the perovskite phase may also have merit.     

The creep behaviour of Synroc and alumina

The creep of Synroc C and alumina in four-point bending in argon was investigated in terms of the relaxed symmetric stress and the reference asymmetric stress; the alumina being used as a reference material. The creep tests were undertaken in the temperature range from 850°C to 1300°C. The rupture behaviour of Synroc at 950°C indicated a high stress exponent, and that the creep ductility was unusual in that the strain increased with increasing test time. A scanning electron miscroscopy examination of Synroc after creep revealed the development of defect-free oxidised surface layers. For Synroc, neither prior exposure to pre-heating in air, nor prior indentation affected the creep rate behaviour. This was attributed to the formation of the oxidised surface layers and the associated healing effects of the damage produced by the indentations.     

Effect of thermal cycling on whisker-reinforced dental resin composites

The mechanical properties of dental resin composites need to be improved in order to extend their use to high stress-bearing applications such as crown and bridge restorations. Recent studies used single crystal ceramic whiskers to reinforce dental composites. The aim of this study was to investigate the effects of thermal cycling on whisker-reinforced composites. It was hypothesized that the whisker composites would not show a reduction in mechanical properties or the breakdown of whisker–resin interface after thermal cycling. Silicon carbide whiskers were mixed with silica particles, thermally fused, then silanized and incorporated into resin to make flexural specimens. The filler mass fraction ranged from 0% to 70%. The specimens were thermal cycled in 5 °C and 60 °C water baths, and then fractured in three-point bending to measure strength. Nano-indentation was used to measure modulus and hardness. No significant loss in composite strength, modulus and hardness was found after 10⁵ thermal cycles (family confidence coefficient=0.95; Tukey's multiple comparison test). The strength of whisker composite increased with filler level up to 60%, then plateaued when filler level was further increased to 70%; the modulus and hardness increased monotonically with filler level. The strength and modulus of whisker composite at 70% filler level were significantly higher than the non-whisker controls both before and after thermal cycling. SEM revealed no separation at the whisker–matrix interfaces, and observed resin remnants on the pulled-out whiskers, indicating strong whisker–resin bonding even after 10⁵ thermal cycles. In conclusion, novel dental resin composites containing silica-fused whiskers possessed superior strength and modulus compared to non-whisker composites both before and after thermal cycling. The whisker–resin bonding appeared to be resistant to thermal cycling in water, so that no loss in composite strength or stiffness occurred after prolonged thermal cycling.     

Prediction model of lifetime for copper pillar bumps under coupling effects of current and thermal cycling

Considering the current induced voids flow will accelerate the creep strain rate and lower the strength of the solder, a current induced activation energy change, ΔQ_e is added in the Anand model. A lifetime prediction model was constructed based on linear damage rule for the current-thermal cycling coupling test. To verify the accuracy of the model, mean-time-to-failure (MTTF) of copper pillar has been experimentally and analytically investigated under the combination of thermal cycling with temperature range of ?40 to 125 °C and a superimposed electric current with current densities of 17.4–22.4 × 10⁴ A/cm². The experimental results reveal that the MTTF sharply decreases with the increasing current density. The acceleration factors are calculated, which is consistent well with the prediction model.     

Effect of thermal cycling on as-quenched and aged nickel-rich Ni-Ti alloy

The effect of Ni₄Ti₃ precipitates on the structure and transformation sequences in Ni-49%Ti alloy has been investigated using internal friction, electrical resistivity and electron microscopy studies. It has been confirmed that in the alloy without precipitates the transformation occurs following the sequence B2 R M on cooling and M B2 on heating with easily distinguished peaks on the internal friction curves and typical behaviour of the electrical resistivity, while the presence of the precipitates brings about complicated internal friction curves indicating either the appearance of two types of martensite or the transformation sequence: B2 ® B2 + R B2 + M M.     

Analysis of thermal cycling by solid mensuration

The plastic flow of material in specimens during thermal cycling was studied. Assuming that the same volume of material migrates during each cycle, a mathematical expression representing the change of volume was derived. This expression could then be used to predict the number of cycles to failure.     

Influence of micro-structural parameters and thermal cycling on the properties of CARDIFRC

This paper gives an overview of the influence of micro-structural parameters on the mechanical properties of CARDIFRC which is a high-performance fibre-reinforced cement-based material. Since its development in 2002, several investigations have been made with a view to examine how its properties vary when its micro-structure is altered and when it is subjected to thermal cycling.     

热循环对片层石墨/铝复合材料的强度和热导率的影响

采用粉末冶金法制备片层石墨增强Al基复合材料(50vol％Gf/6061Al),Gf与Al基体结合紧密,界面处无裂纹、孔洞等缺陷.复合材料在-50～120℃温度范围内分别循环10次、50次、100次和200次,研究不同的循环次数对材料组织和性能的影响.结果 表明,循环不同次数时材料的密度没有明显的变化,但随着循环次数的...     

The role of transient oxides during deposition and thermal cycling of thermal barrier coatings

Abstract

High temperature coating systems, consisting of a René N5 superalloy, a Ni–23Co–23Cr–19Al–0.2Y (at.%) bond coating (BC) and a partially yttria stabilised zirconia (PYSZ) thermal barrier coating (TBC), were thermally cycled to failure for three different pre-oxidation treatments performed for 1 h at 1373 K and a partial oxygen pressure (pO₂) of 20 kPa, 100 Pa and 0.1 Pa, respectively. These pre-treatments resulted in the formation of different thermally grown oxide (TGO) layers prior to TBC deposition with respect to the presence of the transient oxides NiAl₂O₄, θ-Al₂O₃, and Y₃Al₅O₁₂ at the TGO surface. The TGO microstructures after TBC deposition and thermal cycling were investigated with a variety of analytical techniques and compared with those after pre-oxidation. For all pre-oxidation treatments, a double-layered TGO developed on the BC during thermal cycling. The TGO adjacent to the TBC consisted of small Zr-rich oxide crystallites embedded in an Al₂O₃ matrix when the TGO surface after pre-oxidation comprised of Y₃Al₅O₁₂ plus α-Al₂O₃. When the TGO surface constituted of θ-Al₂O₃, the Zr-rich oxide crystallites were embedded in a NiAl₂O₄ spinel layer after thermal cycling. Zr was absent in the oxide layer when the TGO surface prior to TBC deposition was composed of NiAl₂O₄ spinel. The TGO contiguous to the BC consisted in all cases of α-Al₂O₃ with Y₃Al₅O₁₂ crystallites. The roughness of the α-Al₂O₃/BC interface increased for a higher density of Y-rich oxide protrusions (i.e. pegs) along this interface.