High Temperature Thermal Cycling Research Articles

Failure analysis of shot-piston used in squeeze casting process equipment

The failure investigation has been conducted on shot-piston used in injection system of squeeze casting equipment to clarify its failure mechanism. The macroscopic morphology of failed shot-piston showed there were many network cracks on its upper-end surface while the cylindrical surface was seriously worn. Further studies were carried out on the two surfaces respectively. Firstly, the shot-piston upper-end surface was sampled. And the crack distribution and depth were observed. Then, the crack micromorphology was investigated by scanning electron microscope (SEM), and the sampling points inside cracks were analyzed by energy dispersive spectrometer (EDS). The results show the shot-piston upper-end surface produces thermal stress cracks due to the high-temperature thermal cycle, and oxidation occurs in the cracks. The same method was also used for the cylindrical surface failure mechanism analysis. Above all, the cylindrical surface was sampled and the wear morphology was measured. Afterward, the material composition of the bulge on the cylinder surface and the micromorphology were confirmed by SEM and EDS. The results demonstrate the main failure forms are abrasive wear and adhesive wear. The inconsistent thermal deformation of the shot-piston and shot sleeve caused changes in the fit clearance and resulted in friction and wear. Simultaneously, the metal solution and oxygen erode the shot-piston matrix through the furrow, accelerating wear and failure. According to the failure mechanism of different surfaces, shot-piston service life can be extended by optimizing the squeeze casting process, controlling the temperature gradient, and selecting the appropriate fit clearance, which has important engineering significance.

Thermal and mechanical performance of cement paste under high temperature thermal cycles

Concrete is identified in the literature as a suitable material for thermal energy storage applications, with even innovative application potentials such as storage media in concentrating solar power plants. To ensure a suitable heat transfer among concrete components, the binder material of concrete (cement paste) require further research and understanding to this aim. In particular, the thermal stability of cement paste under temperature cycled conditions arises as a research gap. In this study, ordinary Portland and calcium aluminate cement types were selected using a low water-cement ratio. Thermo-mechanical properties were studied before and after 1, 10, and 25 or 50 thermal cycles at 200 °C, 400 °C, 600 °C, and 800 °C. Although ordinary Portland cement paste showed micro-cracking propagation after 25 thermal cycles from ambient temperature to 200 °C and 400 °C, both cement pastes preserved their integrity, being compressive strength higher in ordinary Portland cement. On the contrary, after 25 or 50 thermal cycles at 600 °C and 800 °C, only calcium aluminate cement preserved its integrity, while ordinary Portland cement revealed a fragmentation status. Despite the compressive strength decrease in calcium aluminate paste at 600 °C and 800 °C, as a result of porosity increase, the properties were maintained after 10 thermal cycles. However, thermal conductivity in calcium aluminate paste was reduced nearly 50% after the first cycle at temperatures higher than 200 °C.

Stability investigation of propylene glycol-based Ag@SiO2 nanofluids and their performance in spectral splitting photovoltaic/thermal systems

One main challenge facing nanofluid filters in PV/T systems is their long-term dispersion stability. This work studies the stability of the Ag@SiO2 nanoparticles suspended in propylene glycol (PG)-based fluids for use as optical filters. These nanofluid filters are subjected to high temperature heating test and thermal cycling test to analyze their thermal stability and identify appropriate base fluids. The results of UV–Vis spectroscopy and visual inspection show that both the most concentrated Ag@SiO2/PG + water nanofluid and Ag@SiO2/PG nanofluid exhibit excellent thermal stability when heated to 95 °C and 120 °C, respectively and no agglomeration is observed for exposure to thermal cycling test. A theoretical model with the measured transmittance of the identified Ag@SiO2 nanofluids as the input is introduced to evaluate performance of the nanofluid filtered PV/T system by varying the nanoparticles concentration, optical path-length and concentration ratio. The results indicate that Ag@SiO2/PG + water filter and Ag@SiO2/PG filter for PV/T systems using silicon cells show the capability to increase the economic value of more than 30% at optimum nanoparticles concentration of 12.7 mg/L and optical path-length of 35 mm and 40 mm, respectively, when the concentration ratio varies from 1 to 30 suns.

LC/8YSZ TBCs Thermal Cycling Life and Failure Mechanism under Extreme Temperature Gradients

The purpose of this paper is to study the thermal shock resistance and failure mechanism of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings (LC/8YSZ DCL TBCs) under extreme temperature gradients. At high surface temperatures, thermal shock and infrared temperature measuring modules were used to determine the thermal cycling life and insulation temperature of LC/8YSZ DCL TBCs under extreme temperature gradients by an oxygen–acetylene gas flame testing machine. A viscoelastic model was used to obtain the stress law of solid phase sintering of a coating system using the finite element method. Results and Conclusion: (1) Thermal cycling life was affected by the surface temperature of LC/8YSZ DCL TBCs and decreased sharply with the increase of surface temperature. (2) The LC ceramic surface of the failure coating was sintered, and the higher the temperature, the faster the sintering process. (3) Accelerated life test results showed that high temperature thermal cycling life is not only related to thermal fatigue of ceramic layer, but is also related to the sintering degree of the coating. (4) Although the high temperature thermal stress had great influence on the coating, great sintering stress was produced with sintering of the LC ceramic layer, which is the main cause of LC/8YSZ DCL TBC failure. The above results indicate that for new TBC ceramic materials, especially those for engines above class F, their sinterability should be fully considered. Sintering affects the thermal shock properties at high temperature. Our research results can provide reference for material selection and high temperature performance research.

Thermo-oxidative aging and thermal cycling of PETI-340M composites

Polyimide composites (PETI-340M) were fabricated and subjected to high-temperature aging and thermal cycling to evaluate resistance to degradation. Mechanical-degradation mechanisms and kinetics depended on aging temperature. Aging at 232°C resulted in strength loss due to polymer degradation, while intra-tow cracking was the dominant mechanism during aging at 288°C. Composite panels subjected to thermal-cycling fatigue (−54°C to 232°C) retained mechanical properties without microcracking. However, in regions containing pre-existing fabrication-induced defects (primarily voids), intra-tow microcracks were observed after thermal cycling. Unlike some polyimide composites (PMR-15), oxidative aging effects during thermal cycling were negligible. The thermo-oxidative stability and the retention of mechanical performance after thermal cycling indicates potential for long-term, high-temperature structural applications.

Heat-affected coarsening of β grain in titanium alloy during laser directed energy deposition

The heat-affected coarsening of β-grains in titanium alloy produced by additive manufacturing (AM), which would be important for the achievement of fine β-grain like forging, was completely neglected in the past. Here, we reported that the significant coarsening of equiaxed β-grain of Ti6Al4V happened under the instantaneous high-temperature (above β-transus) thermal cycling during laser directed energy deposition process. Especially, the coarsening becomes more striking in the cases of smaller initial β-grain, larger energy density and higher preheating-temperature. Meanwhile, a modified model used to predict the size of the coarsened β-grain of AM titanium alloy was proposed. These findings provide a more comprehensive understanding of the β-grains of AM titanium alloy and a significant guidance for the composition design of AM titanium alloy with fine equiaxed β-grains.

Influence of high-temperature thermal cycles on the pore structure of red sandstone

Influence of high-temperature thermal cycles on the pore structure of red sandstone

Mechanical test of granite with multiple water\u2013thermal cycles

To study the influence of thermal shock caused by water-cooling on the physical and mechanical properties of high-temperature granite, granite was subjected to an increasing number of high-temperature (300 °C) water-cooling and thermal shock treatment cycles, and static mechanical experiments were carried out on the treated granite. The results support the following conclusions: (1) thermal shock causes an increase in the number and size of the pores and cracks within the granite; thus, its volume expands, density decreases, water absorption rate increases, and P-wave velocity decreases. (2) With an increase in the number of thermal shocks, both the compressive strength and tensile strength of the granite decrease, and there is a linear relationship between the compressive strength and tensile strength. (3) With an increase in the number of thermal shocks, the plasticity of the granite increases and its resistance to deformation weakens, which is manifested as a decrease in both the compressive modulus and tensile modulus of the granite. After 15 cycles of thermal shock, the compressive elastic modulus and tensile modulus of the granite decreased by 25.18% and 46.76%, respectively. (4) The m and s values of the damaged granite were calculated based on the Hoek–Brown empirical criterion, and it was found that both of these parameters decrease with the increase in the number of thermal shocks. The calculation results can provide a reference for engineering rock mass failure.

Transformation of non-metallic inclusions in steel under explosive loading and heating

Purpose. The goal of the work was to study phase and structural transformations in nonmetallic inclusions under pulsed loading and subsequent heating.Methodology. Dynamic loading of the samples of steels was carried out according to the scheme of throwing a thin plate (ihe pressure 80...90 GPa, the deformation rate was 100 sec-1, the exposure time was 1,5 · 10-6 sec). After pulsed loading, some of the samples were annealed or thermal cycling. The studies were carried out by methods: metallographic ("Neophot-21"), electron microscopic (JSM-35), petrographic, quantitative metallography ("Quantimet"). Findings. The features of the phase and structural transformations in nonmetallic inclusions under pulsed loading and subsequent heating (high-temperature annealing, thermal cycling) were investigated. It has been found that the explosive action, which creates stresses near the inclusions, influence on the nature of phase transformations during subsequent heating. Originality. The main phase and structural transformations in nonmetallic inclusions that occur at the moment of pulsed loading (polymorphic transformations, transition to an unstable state, amorphization, decomposition of solid solutions) have been determined. The effect of explosive action on transformations in inclusions during subsequent high-temperature annealing and thermal cycling (transition to a more stable state, "devitrification", diffusion crushing, separation of "satellite" particles) was shown.Practical value. The use of the results obtained will make it possible to develop modes of pulsed pressure treatment, as well as complex treatment (explosion + high-temperature annealing, thermal cycling), which allow influencing the mechanical and operational properties of steels for various purposes.

Directed energy deposition additive manufacturing of a Sc/Zr-modified Al–Mg alloy: Effect of thermal history on microstructural evolution and mechanical properties

Recently, laser additive manufacturing (LAM) of Al–Mg–Sc–Zr alloys has been considered an important method for developing a new generation of high-performance Al alloys. However, one of the key differences between LAM and conventional casting/wrought processes is that it has a unique combination of rapid solidification and in-situ solid-state transformation induced by repeated thermal cycling during deposition. In addition, owing to its near-net shape characteristics, subsequent plastic deformation processing is typically not an option to improve the as-built microstructure. To gain insight into the effect of the complex thermal history during LAM on the microstructural evolution and mechanical properties of the novel alloy systems, an Al–Mg–Sc–Zr alloy was processed via laser-directed energy deposition (L-DED) using a substrate with air cooling (AC) or water cooling (WC). The results show that the solidification microstructure was closely related to the dynamic solidification conditions in the molten pool, which promoted the transition from an equiaxed grain structure at low cooling rate (AC) to a heterogeneous grain structure at high cooling rate (WC). Furthermore, in-situ precipitation occurred during the repeated high-temperature thermal cycling in the AC sample, while it was effectively suppressed in the WC sample by lowering the peak temperature during thermal cycling. After aging, the yield strength of the WC sample was enhanced to ~2 times that of the AC sample, while the uniform elongation was still comparable to that of the AC sample. To achieve good mechanical properties for L-DED-processed Al–Mg–Sc–Zr alloys, it is crucial to conduct integrated control of the thermal history during both rapid solidification and in-situ precipitation.

High temperature creep behavior of a cast polycrystalline nickel-based superalloy K465 under thermal cycling conditions

Turbine blades in aircraft engines may suffer serious microstructural degradation and even failure due to sharp overheating during service. In this study, a microwave heating creep testing rig was designed and developed to conduct the high temperature thermal cycling creep experiments, to reveal the overheating effect on the creep behavior of a conventionally cast Ni-based superalloy K465. The thermal cycling creep experiments were conducted under (900 ℃/30 min–1100 ℃/3 min)/70 MPa, combined with the comparative isothermal creep references under 900 ℃/70 MPa and 1100 ℃/70 MPa. The thermal cycling creep exhibited unique characteristics namely short creep life, high creep strain rate and high fracture strain. During the thermal cycling creep, secondary γ′ precipitates dissolved rapidly at higher creep temperature, while recovered partially at lower creep temperature. The obvious microstructural degradation of secondary γ′ precipitates was primarily responsible for the short life of the thermal cycling creep. When secondary γ′ precipitates recovered and coarsened, early shearing of the γ′ phase by entrapped interfacial dislocations occurred, especially at the concave locations of the secondary γ′ precipitates. The evolution of dislocations was mainly responsible for the high minimum creep strain rate of the thermal cycling creep. The creep voids/cracks initiated quickly and located at the interface of M6C carbides and γ/γ′ eutectic pools in the interdendritic regions and grain boundaries during the thermal cycling creep, and finally caused the intergranular fracture.

Investigation and Composition Characterization of a “NiTi-like” Alloy Combining High Temperature Shape Memory and High Entropy

New high temperature shape memory alloys with five or more elements are under development and present attractive performances for several functional applications. These active metallic materials are called high entropy and high temperature shape memory alloys (HE-HT-SMAs). This work deals with the characterization of an alloy that combines high temperature shape memory effect and high entropy effect features, a NiCuTiHfZr alloy. The evolution of the phase transformation and the shape memory effect during thermal fatigue was compared with a ternary alloy NiTiZr. Ingots were prepared in a cold crucible and alloys were characterized after thermal cycling at 600 K without a protective gas atmosphere. Optical microscope, X-ray diffraction, and scanning electron microscopy observations showed the presence of martensite in this unpublished alloy at room temperature. The differential scanning calorimetry (DSC) tests showed that martensitic transformation takes place at high temperature. High temperature thermal cycling was performed during a three-point bending tests under constant load without a protective atmosphere. Thermomechanical results showed that high entropy effects increase the operating behavior at high temperature. Hence this new composition of NiCuTiHfZr alloy can be used as an actuator for aerospace and aeronautic application.

Effect of Multilayer and Multi-pass Welding on Microstructure and Properties of Al–Mg Alloy Welding Joint

Three-layer and four-pass metal inert gas welding tests were carried out on 5A01 alloy sheet by using 5B01 wires as filler material. The research results showed that the thermal cycle of the next weld would affect one or even more welds that have been welded. The short-term high-temperature thermal cycling made different weld regions go through different peak temperatures and cooling times, which made the structure and properties of the weld show some inhomogeneity. The fine-grained layer was formed in the fusion zone due to the great degree of supercoiling, and fine Al3Zr particles had become the nucleating center of the inhomogeneous nucleation. Grain boundary remelting caused by high welding temperature resulted in the appearance of coarse grain at the interface of weld beads. In addition, the grain growth direction was affected by the heat dissipation direction, and the center of each weld bead was typical rapidly cooled casting structure.

Evolution of structures and optical properties of vanadium oxides film with temperature deposited by magnetron sputtering

In this study, mid infrared optical modulation property of VOx films with temperature was researched. VOx film which contain both VO2 and V2O5 was deposited on Al2O3 substrate by radio frequency magnetron sputtering. The mid infrared transmittance undergoes two reductions when increasing the temperature to 590 °C, the first reversible reduction around 68 °C as the phase transition of VO2 and the second irreversible gradually reduction starting around 350 °C because the oxidation state changed from V2O5 to VO2. The transmittance increased from 5.49% to 70.29% when cooling the temperature around 54℃. The film has the reversible 64% optical modulation around 60 °C during the second thermal cycling and keep stable even increased the temperature higher than 550 °C. The difference caused by high temperature thermal cycling in surface morphology structures, and chemical composition, were characterized by AFM, XRD, Raman, and XPS. The process of phase transition and the oxidation state changed during the thermal cycles were monitored with temperature dependent Raman spectra. This study provides new information about the transition between different structures and oxidation states of VOx film and a good candidate for infrared thermochromic window.

High-Temperature Thermal Conductivity and Thermal Cycling Behavior of Cu–B/Diamond Composites

Diamond particle-reinforced copper matrix (Cu/diamond) composites are currently considered as a promising thermal management material due to their high thermal conductivity and matching coefficient of thermal expansion (CTE) with the semiconductor. In this article, the Cu– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x\text{B}$ </tex-math></inline-formula> /diamond ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x = 0.1$ </tex-math></inline-formula> –1.0 wt%) composites with 67% diamond volume fraction were produced by gas-pressure infiltration. The thermal conductivity of the Cu–B/diamond composites decreases with the increasing temperature from 323 to 673 K, owing to the property change of the composite components. The samples were subjected to 100 thermal cycles from 218 to 423 K to investigate the long-term stability of the Cu–B/diamond composites. The results suggest that the interface structure evolution plays a critical role in determining the high-temperature thermal conductivity and thermal cycling behavior of the Cu–B/diamond composites. By measuring the thermal properties before and after thermal cycling, we found that the Cu–0.5wt%B/diamond composite has the best thermal stability. After 100 thermal cycles, the room temperature thermal conductivity remains almost unchanged at ~740 W/mK, and the CTE increases slightly from 4.88 to 4.97 ppm/K. This article expands the understanding of the thermal properties of the Cu-B/diamond composites and provides a fundamental basis for their electronics packaging applications.

Effect of boron on the microstructure and mechanical properties of Ti-6Al-4V produced by laser directed energy deposition after heat treatment

The nearly rapid solidification and high-temperature thermal cycles associated with laser directed energy deposition of titanium alloys using laser solid forming (LSF) lead to the formation of coarse prior β columnar grains and continuous coarse-grain-boundary α (αGB) phases, which result in anisotropic properties and poor ductility. The influence mechanisms of trace B (up to 0.3 wt. %) on the solidification, solid state transformation, and tensile properties of LSFed Ti-6Al-4V after solution and aging treatment were studied using thermodynamic calculations. With an increase in B content, the size of prior β grains decreased owing to the growth-restricting effect it caused during the solidification and the Zener pinning caused by TiB during reheat cycles and heat treatments. The continuous coarse αGB phases were almost eliminated owing to the discontinuous distribution of TiB between the dendrites, and the length and aspect ratio of intragranular α phases were gradually reduced. Moreover, both ultimate tensile strength and yield strength increased, fracture elongation decreased, strength anisotropy decreased, and elongation anisotropy initially increased and then decreased significantly. The findings in this study will promote the development of new Ti alloys befitting additive manufacturing technology.

Microstructural Stability of Ti based Composites Fabricated by Spark Plasma Sintering

In our previous study, the effects of TiC heterogeneous nucleation site particles on formability and microstructure of additive manufactured (AMed) Ti-6Al-4V products were studied. It was found that the addition of TiC particles decreased the grain size of primary β phase in AMed Ti-6Al-4V samples, since TiC particles act as heterogeneous nucleation sites. It is also found that the density of AMed Ti-6Al-4V samples could be increased by addition of TiC particles. It is expected that solid-state β-grain growth by the high temperature thermal cycles associated with layer-by-layer manufacturing can be suppressed by the pinning effect of TiC heterogeneous nucleation site particles. In this study, the pinning effect of heterogeneous nucleation site particles on microstructure of Ti at elevated temperatures is studied. For this purpose, Ti-0.3vol%TiC samples fabricated by spark plasma sintering (SPS) are used as the model materials, and microstructure and hardness of the samples heat treated at elevated temperatures are studied.

Mechanical and Thermal Properties of UHPC Exposed to High-Temperature Thermal Cycling

The effects of high-temperature thermal cycling (temperatures up to 500°C) and steel fiber contents on the mechanical and thermal properties of ultrahigh-performance concrete (UHPC) containing polypropylene (PP) fibers were investigated in this study. The different maximum temperatures for thermal cycling included 300, 400, and 500°C. The mechanical properties, including the compressive strength and tensile strength, and thermal properties, including the unit weight and thermal conductivity, of the UHPC specimens were measured. The experimental results indicated that the compressive strength, tensile strength, unit weight, and thermal conductivity decreased as the temperature increased to 500°C. Test results showed that for each maximum temperature, the reduction of the thermal conductivities from one to six thermal cycles was not significant. The thermal conductivity of the UHPC decreased as the unit weight of the UHPC decreased, and the thermal conductivity also decreased as the compressive strength of the UHPC decreased. Scanning electron microscopy (SEM) analysis showed that the microstructures of the UHPC specimens exposed to high temperatures contained voids due to the PP fiber melting. The porosity of the UHPC specimens increased as the maximum temperature of the thermal cycles increased, which decreased the unit weights and thermal conductivities of the UHPC specimens. Moreover, the porosity at a temperature of 500°C increased by 60.0, 74.5, and 123.4% for steel fiber contents of 1.0, 1.5, and 2.0%, respectively. It might be due to incompatible thermal expansion between the concrete matrix and steel fiber.

Mechanisms of thermal cycling damage in polycrystalline Sn-rich solder joints

Solder joints will experience elevated temperatures during operation due to resistive heating and ambient conditions. Device components have different thermal expansion characteristics, leading to straining of the solder joint and development of surface damage features. The anisotropic thermal expansion of βSn grains and discrepancy between the thermal expansion of intermetallic compounds causes degradation to be localized near grain boundaries and phase interfaces. Three experiments were conducted to investigate thermal effects on solder joint microstructure. Interrupted low temperature aging revealed the formation and movement of grain boundary ledges and uninterrupted thermal aging confirmed that the ledges formed during the cooling cycle of the experiment. Finally, high temperature thermal cycling demonstrated the acceleration of surface damage that accompanies an increase in peak temperature and cycling frequency. The orientation of the c-axis of the Sn matrix grains proved to be the critical feature controlling the direction of grain boundary ledge migration and type of surface deformation surrounding Cu6Sn5 intermetallic needles.

TEM study of the effect of high-temperature thermal cycles on the stability of the Y-Al-O oxides in MA956 ODS steel

MA956, a commercial ferritic grade of Oxide-Dispersion-Strengthened (ODS) steel, was investigated using transmission electron microscopy (TEM) to evaluate the influence of high-temperature thermal cycles on the nanometric dispersed oxides. Analyses of the oxide size distribution were carried out on foils from the as-received MA956 and following treatment at 1285 °C for one hour, and show that growth of the oxides has occurred under the thermal cycle. Implications for the oxide stability in the steel matrix are discussed, in the light of the oxide chemical composition.