High Temperature Capability Research Articles

Impact of boron as an alloying addition on the microstructure, thermo-physical properties and creep resistance of a tungsten-free Co-base γ/γ′ superalloy

While boron is added to many structural alloys primarily as a grain-boundary strengthener, it has myriad other implications on the microstructure and thermophysical properties of these alloys. In the present study, we report these effects by varying boron addition in the range of 0.02 at.% to 0.8 at.% on the microstructure, thermo-physical properties and the creep resistance of tungsten free, γ/γ′ base Co–30Ni–10Al–5Mo–2Ta–2Ti (at.%) polycrystalline superalloy. Without boron addition, the plastic strain during creep at 850 °C is primarily accommodated through grain-boundary decohesion, often enhanced by severe oxygen attack along the grain boundaries. The addition of boron alleviates the poor grain-boundary cohesivity while inhibiting internal oxidation. An increase in the solvus temperature with boron addition was found, leading to an increase in the high-temperature capability of this alloy (∼40 °C). However, a concurrent decrease in the alloy's melting point has been observed. Coupled with improved grain-boundary cohesivity and larger grain size, improvement in creep resistance by almost an order of magnitude could be achieved. While at low amounts of boron (0.02–0.08 at.%) borides do not form, indicating solid solubility of boron within the bulk alloy, at high boron contents (0.2–0.8 at.%), Co and Mo rich boride forms primarily along the grain boundaries. These borides are surrounded by a distribution of fine secondary γ′ precipitates around them. In contrast, borides in Co–Al–W alloys promote precipitate free zones (PDZ), causing deterioration of mechanical properties. The beneficial effect of boron along grain-boundaries, both in elemental form and in the form of borides, has been highlighted in the present study which paves way for optimizing boron addition in other alloys of this class.

Investigation of Corrosion in Bolted Flanged Joints Using a Novel Experimental Setup

The second most common cause of hydrocarbon leakage is corrosion in offshore platforms. In seawater and hydrocarbon services, bolted flange joints can be susceptible to corrosion on the flange face. Flanges connect pipes, valves, pumps, and other equipment to form a piping system. In flanged joints, two flanges are bolted together with a gasket between them to provide a seal. The current research considers corrosion in bolted flanged gasketed joints and proposes a new approach to quantify corrosion at the gasket and flange interface. According to the literature, both crevice corrosion and galvanic corrosion widely occur in bolted flanged gasketed connections, which create paths to leakage of the pressurized fluid. Leakage failure in bolted flanged gasketed joints can cause hazards to the environment and human safety. Corrosion in bolted gasketed joints was investigated in other papers and reports. Still, these studies did not consider the influence of the operating conditions. Fluid flow, pressure, pH, conductivity, temperature, and gasket contact pressure are some parameters to consider.To achieve this goal, a novel experimental setup - mimicking an industry-standard NPS 2 bolted flange connection - is introduced to examine the corrosion behavior of the contact surface between the flange and gasket. The setup enables monitoring and recording of the corrosion parameters under the influence of service conditions (gasket contact pressure, pH, salinity, temperature, fluid flow, and fluid pressure) during the corrosion tests. In a second step, the influence of the service conditions on corrosion will be studied. Two levels of temperature (25 o C and 85 o C), gasket contact pressure (4 MPa and 35 MPa), and flow rate (1.4 cm. s-1 and 4.5 cm. s-1) are considered in the study. The flange material selected in this study is stainless steel 304/304L since it has a wide application in the industry. Flexible graphite materials, commonly used due to their chemical resistance, high-temperature capability, low cost, and good sealing properties, are used in the corrosion tests. Two direct current electrochemical test techniques, polarization resistance (Rp) and potentiodynamic anodic polarization, are carried out, according to ASTM G5, to measure the corrosion rate in addition to other quantification methods based on visual observations and mass loss. These tests are conducted using the novel designed setup that consists of a working electrode (flange material), a reference electrode (Ag/AgCl), and an auxiliary electrode (a stainless-steel rod). The synthetic seawater solution recommended in ASTM D1141 is used for the corrosion tests. In a final step, the corroded surfaces of the specimens are examined via some of the following available techniques; confocal laser microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray microscopy (EDS/EDX), and X-ray powder diffraction (XRD) techniques. Confocal microscopy is used to visualize the morphology of the damaged zones on the surface, and localize and quantify the crevices volume caused by corrosion, respectively. SEM and XRD analysis can reveal the scale morphology and phases present on the corroded plate surfaces. Comparing the results of the electrochemical tests and the microscopic studies will identify the influence of operating factors on the corrosion at the gasket-flange interface.Preliminary tests were performed to check the applicability of the novel setup for studying corrosion behaviour between gaskets and flanges and solve initial setup problems to get reproducible results. In the current research, the corrosion behaviour is studied under dynamic conditions. The majority of other works consider only the static condition, so it is important to run some preliminary tests to shakedown the rig and fixture and resolve unanticipated issues. First attempts failed due to noisy polarization curves that could not be used for corrosion analysis. After several experiments on small samples, it was decided to use filter paper immersed in a 3.5% NaCl solution as a salt bridge to reduce the distance between the reference and working electrodes in the setup. This resulted in smooth polarization curves useful for further corrosion analysis (Fig. 1).The novel designed bolted flange joint setup allows corrosion monitoring and characterization under dynamic operating conditions for the first time. Figure 1

SPS TECHNOLOGIES AEREX 350

Abstract SPS Technologies Aerex 350 is a proprietary high-strength, corrosion-resistant nickel-based superalloy that is suitable for demanding applications up to 730 °C (1350 °F). It has the highest temperature limit of the three SPS superalloys. Like MP35N and MP159, this alloy not only undergoes the multiphase reaction, but also benefits from two additional strengthening mechanisms. Elements are also added to the chemical composition to cause precipitation of the gamma prime phase with higher temperature capability than MP159. Because this alloy is used at even higher temperatures than MP159, elements are added to the chemical composition to also cause the precipitation of eta phase during thermal treatments. This phase contributes to notch toughness at elevated temperatures. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance. Filing Code: Ni-780. Producer or source: SPS Technologies, Inc.

4H-SiCδn-i-p Extreme Ultraviolet Detector With Gradient Doping-Induced Surface Junction

Extreme ultraviolet (EUV) detectors are key components required in many critical applications. In this work, a high-performance 4H-SiC <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta \text{n}$ </tex-math></inline-formula> -i-p EUV detector with gradient doping-induced surface junction is designed and fabricated. The detector demonstrates ultra-low leakage current and excellent photo-response uniformity across the ~6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> photo-sensitive area. Under photovoltaic operation mode, the detector exhibits high responsivity of 0.104 A/W and corresponding quantum efficiency of 960%@13.5 nm, which are close to the theoretical limit. Meanwhile, the equivalent noise power of the device under 0 V bias is determined to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.35\times {10}^{\text {-12}}$ </tex-math></inline-formula> W by 1/f noise test, proving that the device has a very low noise level and corresponding high detectivity. In addition, the high-temperature working capability and radiation-resistant performance of the EUV detector are preliminarily verified.

Assessing the electrical property of carbon nanotube reinforced oxide ceramic matrix composites produced by ceramic injection moulding

Owing to its remarkable properties, multiwalled carbon nanotubes (MWCNTs) are attracting the interest for realization of sensors. The potential of MWCNTs for high temperature sensing applications was investigated by integration within reinforced aluminium oxide ceramic composite. MWCNTs up to 2 wt% were mixed with reinforced aluminum oxide ceramic composite using solution mixing method to ensure good homogeneilty of the oxide ceramic composite powders. Specimens were realized using ceramic injection moulding process (CIM) followed by debinding and sintering procedures. The topography of specimens were examined using atomic force microscopy (AFM). Electrical measurements were also carried out. The results show good demouldability at high MWCNTs concentration and homogenous distribution of the MWCNTs within the oxide ceramic matrix. AFM images illustrate the reduction of surface roughness by increasing the MWCNTs content which demonstrates the role of MWCNTs to improve the fracture resistance of the oxide ceramic matrix composite. As well, the electrical resistance of the feedstocks were reduced sharply. After sintering process, the resistance range drops enormously from M Ω to reach 12.1 Ω at low MWCNTs content; which make them suitable to be as electrode with high temperature capability. The electrical resistance temperature dependency shows a negative temperature coefficient behaviour with negligible resistance change.

To drill or not to drill? Creep of an oxide‐oxide composite with diamond‐drilled effusion holes at elevated temperature

Ceramic matrix composites (CMCs) are prime candidates for use in aircraft engines. Yet even with their high-temperature capabilities, many CMC components will need cooling. Film cooling technique requires rows of small holes through the component surface. Effects of multiple small holes on tensile stress-strain and tensile creep performance of an oxide-oxide CMC consisting of Nextel 720 alumina-mullite fibers in a porous alumina matrix were evaluated at 1200°C. Test specimens included 17 holes with a .5 mm diameter in the gage section. The holes were precision drilled using diamond coated drill bits. The presence of diamond-drilled holes noticeably lowered tensile properties and degraded creep performance of the CMC. Our earlier study considered the effects of small holes drilled using a CO2 laser on the tensile properties and tensile creep resistance of this composite. The presence of laser-drilled holes also considerably lowered the creep resistance of the Nextel 720/alumina CMC. In both cases the reductions in tensile strength and creep resistance are due to damage caused to composite microstructure by hole drilling. However, different drilling techniques result in different microstructure degradation mechanisms. Damage to the CMC microstructure caused by these two drilling techniques and implications for mechanical performance and durability are discussed.

Interaction of beryllium with 316H stainless steel in molten Li2BeF4 (FLiBe)

The increased demand in renewable energy resources has led to a renewed interest in nuclear reactors including a new generation of molten salt reactors. One of the issues encountered in handling of molten chloride or fluoride salts is the inability of metals to form and retain a protective oxide surface layer, generally chromium oxide. The low chromium content, nickel-based alloy INOR-8, later marketed as Hastelloy N, was specifically developed to contain molten fluorides. This alloy had some deficiencies, but its composition resulted in it incurring far less chromium depletion by the molten fluoride salts than alloys like 316 stainless steel. For the next generation of molten salt reactors, an alloy with pressure vessel code approval and higher temperature capability than Hastelloy N is required. Consequently, several reactor designers have reportedly chosen to build the reactor containment vessel from 316H stainless steel. In order to minimize corrosion of the stainless steel by the molten fluoride salt (2LiF-BeF2), it is proposed to add beryllium metal to the salt to react with impurities and provide a means to lower the oxidation potential thus making the salt less corrosive. However, there is a concern whether the beryllium would react with components of the stainless steel. To address this concern, static capsule tests were conducted in which selected amounts of beryllium were added to capsules containing 2LiF-BeF2 (FLiBe) salt and 316H stainless steel and Hastelloy N samples. Following exposure, the samples were cleaned and examined using a variety of analysis techniques including, optical microscopy, SEM-EDS, XPS, LIBS, XRD and EPMA. Tensile samples were also exposed in capsules, and those were subjected to tensile testing. It was found that for the level of beryllium additions used in this study, intermetallic compounds were formed which could be detrimental to the long-term performance of the 316H stainless steel.

Control of High-Temperature Static and Transient Thermomechanical Behavior of SiMo Ductile Iron by Al Alloying

Silicon and molybdenum (SiMo) ductile iron is commonly used for exhaust manifolds because these components experience thermal cycling in oxidizing environment, which requires resistance to fatigue during transient thermomechanical loads. Previous studies have demonstrated that alloying elements, such as Al, to SiMo ductile iron reduces the amount of surface degradation during static high-temperature exposure. However, deterioration of sphericity of the graphite nodules and a decrease in ductility could affect the tendency of cracking during thermal cycling. In this article, the effect of Al alloying on static and transient thermomechanical behavior of SiMo ductile iron was investigated to optimize the amount of Al alloying. A thermodynamic approach was used to confirm the effect of the Al alloying on the phase transformations in two SiMo cast irons, alloyed by 1.8% Al and 3% Al. These two alloys were cast in a laboratory along with the baseline SiMo ductile iron. Several experimental methods were used to evaluate the dimensional stability, physical properties, static oxidation, and failure resistance during constrained thermal cycling testing to compare their high-temperature capability. Experimental results verified that Al alloying increases the temperature range and decreases volume change during eutectoid transformation, which together with enhancement of oxidation protection improved the dimensional stability. Thermocycling tests showed that the number of cycles to failure depends on the amount of Al alloying and the applied high-temperature exposure during each cycle. SEM/EDX, high-resolution TEM and µCT analysis were used to verify the mechanism resulting from the Al alloying protection. It was shown that an optimal level of Al alloying for balancing oxidation and thermal cracking resistance depends on thermomechanical conditions of application.

Contemporary Materials Issues for Advanced EB-PVD Thermal Barrier Coating Systems

AbstractThe key issues for thermal barrier coating (TBC) development are high temperature capability and durability under thermal cyclic conditions as experienced in the hot section of gas turbines. Due to the complexity of the system and the interaction of the constituents, performance improvements require a systems approach. However, there are issues closely related to the ceramic top coating and the bond coat, respectively. Reduced thermal conductivity, sintering, and stresses within the ceramic coating are addressed in the paper as well as factors affecting failure of the TBC by spallation. The latter is primarily governed by the formation and growth of the thermally grown oxide scale and therefore related to the bond coat. A strategy for lifetime assessment of TBCs is discussed.

Microencapsulation of high temperature metallic phase change materials with SiCN shell

Metallic phase change materials (PCMs) have the advantages of large phase change latent heat, high heat storage density and broad application prospects in various high temperature industrial waste heat recovery and utilization. However, due to the strong corrosion of molten metal at high temperature, appropriate packaging technology is the prerequisite for the promotion and application of metallic PCMs. In this research, a high temperature PCM microencapsulating technology with SiCN shell and a new microencapsulation method was proposed. The high temperature microencapsulated phase change materials (MEPCMs) with the core–shell mass ratios of 5:1, 4:1 and 3:1 were prepared by “solvent evaporation-heating curing” method, using SiCN cured by organic polysilazane (OPSZ) as heat resistant shell material and Al-Si particles as core PCMs. The mechanisms of shell formation and coating of OPSZ were studied experimentally, as well as the material properties and thermal performance of MEPCMs. With the increase of temperature, OPSZ gradually formed a dense SiCN shell on the surface of Al-Si particles. The experimental results showed that MEPCMs with the core–shell mass ratio of 4:1 had a high phase change temperature (571.9 °C-573.7 °C) and good heat storage capability (281.2 J/g-282.9 J/g). SiCN shell was conducive to maintain a complete core–shell structure, and exhibited excellent thermal resistance and oxidation resistance to protect inner core materials during thermal cycles. Therefore, the prepared microcapsule was a potential heat storage material, which provided a new idea for developing microencapsulation method of high temperature PCMs.

Investigation of PEEK Lined Pads for Tilting-Pad Journal Bearings

Tilting-pad journal bearings are widely used in industry to support rotating shafts due to their high dynamic performance. The operating limits of these bearings are mainly represented by the maximum permissible temperature of the lined materials of the pads and by the minimum thickness of the oil-film under which mixed lubrication can occur. The current trend in bearing development sees the adoption of innovative materials in the production of the pads, that provide higher load capacity, higher temperature capability and greater fatigue resistance. In this paper, the static characteristics of bearings lined with different materials, will be investigated. The temperature distribution in the bearing will be evaluated by means of a full 3D thermal model whereas the deformation of the pads will be evaluated by means of a finite element model. At the end, the permissible operating range in terms of load and speed will be defined for each material by considering the limits on the maximum temperature, permissible mechanical stress and minimum oil-film thickness.

Fabrication and Characterization of Semi-Crystalline and Amorphous Dielectric Polymer Films for Energy Storage

Dielectric polymer films are energy storage materials that are used in pulse power operations, power electronics and sustainable energy applications. This paper reviews energy storage devices with focus on dielectric film capacitors. Two prominent examples of polymer dielectrics Polyetherimide (PEI) and Poly (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride) (THV) have been discussed. Polyetherimide (PEI) is an amorphous polymer recognized for its high-temperature capability, low dielectric loss and high dielectric strength. THV is a semi-crystalline polymer with high dielectric constant, high-temperature capability and charge-discharge efficiency. The primary focus of this paper is to introduce the reader to the fabrication procedures and characterization techniques used in research labs for processing of dielectric polymers. The fabrication and characterization process of both polymers has been discussed in detail to shed the light on experimental process in this area of research.

Effect of repeated thermal cycle on compressive properties of cyanate ester/quartz-based composites

The continuous fibre reinforced polymer composites are used in electronic circuits and radar radomes of defence aircraft due to lower transmission loss in the broadband microwave frequency region. Quartz fibre-reinforced cyanate ester composites are one of the best-suited materials for the radome structure of an aircraft offering exceptional electromagnetic transparency in varying operational temperatures. Moreover, this material possesses high-temperature capability with excellent mechanical and dielectric properties. The radome structure usually undergoes multiple thermal cycles during fabrication. In this work, to determine the compressive strength, a quartz/cyanate ester laminate was prepared with repeated thermal infusion followed by final curing (CE/Q_M) using resin film infusion (RFI) technique. The volume fraction of fibre, resin and void fraction were evaluated using the resin-burn off method. Finally, Ultrasonic C-scanning, a non-destructive quality evaluation and raster scanning using a multi-axis squirter system was carried out to detect and characterize the defects induced in the laminate. These data were compared to a sample produced with regular infusion followed by a curing cycle (CE/Q_S). The compressive strength of CE/Q_M (372.48 MPa) is measured to be 12% more than that of CE/Q_S (332.084 MPa). This is attributed to increased crosslink density in CE resin and strong interfacial adhesion between the resin and the fibre in the latter due to multiple thermal infusion cycles.

Enhancement of high-temperature dielectric energy storage performances of polyimide nanocomposites utilizing surface functionalized MAX nanosheets

High-temperature dielectric polymers have a broad application space in film capacitors for high-temperature electrostatic energy storage. However, low permittivity, low energy density and poor thermal conductivity of high-temperate polymer dielectrics constrain their application in the harsh-environment electronic devices, especially under elevated temperatures. Here, the combination of dopamine functionalized MAX (Ti3AlC2) nanosheets and a polyimide (PI) matrix offers a feasible strategy to prepare high-temperature polymer nanocomposites with improved dielectric and thermal performances. The surface functionalized MAX nanosheets with dopamine has guaranteed both the increase of dielectric constant and breakdown strength, leading to improved energy storage capability. As a result, the nanocomposite with 3 wt % functionalized MAX exhibits an enhanced energy density of 2.60 J/cm3 at 30 °C, and the nanocomposite with 1 wt % fillers possess an energy density of 1.19 J/cm3 at 100 °C, more than 1.32 and 1.18 times that of neat PI films (1.97 J/cm3 at 30 °C and 1.01 J/cm3 at 100 °C). In addition, an improved in-plane thermal conductivity of 0.55 W/(m·K) is obtained for PI based nanocomposite with 7 wt % MAX@dopa, which is much higher than that of pure polymer (0.18 W/(m·K)). Our results show that surface modified MAX nanosheets can be used to construct polymer-based nanocomposites with excellent high-temperature energy storage capability and thermal properties.

Micromechanical analysis and theoretical predictions towards thermal shock resistance of HfO2-Si environmental barrier coatings

As HfO2-doped Si bond coat acts a pivotal part in application of progressive environmental barrier coating (EBC) system owing to improving the high-temperature capability and creep properties of bond coat, it is essential to control the doping content and to balance the mechanical and thermal properties of doped coatings challenge in terms of upgrading service life and operating temperature of EBC system. In this study, the physical properties and thermal shock performance at 1723 K of HfO2-Si composite coatings with three different compositions were investigated via first-principle calculations and micromechanical model. Evidently, the composite coatings deposited by magnetron sputtering exhibit a better resistance towards crack initiation and propagation than pure Si bond coat up to 100 h thermal cycling time. Such improvement is attributed to the dispersion toughening effect caused by the characteristic structure of dispersed HfSiO4 particle within cristobalite “mortar”. With thermal cycling, the continuous Ostwald ripening of HfSiO4 particles decreased the elastic modulus and effective thermal expansion coefficient gap at room and high temperature of composite coatings, which was advantageous to thermal shock resistance. Unfortunately, as a consequence of excessive volume expansion during particle ripening, the composite coatings encountered varying degrees of interface separation after 100 cycles and hence not protective anymore. The results suggested that the further modification for low-frequency vibration patterns of HfSiO4 and realizing the interfacial metallurgical bonding can reduce the thermal expansion coefficient of HfO2-doped Si composite coatings and strengthen interface adhesion.

Effects of synthesis methods on the physicochemical properties and Hg0 capture capability of MnO2-CeO2 mixed oxides

This study illustrated the effects of synthesis methods, namely, co-precipitation (CP), hydrothermal (HT), and ethylene glycol-assisted solvothermal method (EG), on the physicochemical properties and Hg0 capture capability of MnO2-CeO2 mixed oxides. For the samples prepared using CP and EG methods, a downward trend in the Hg0 removal efficiency from ca. 100% to lower than 40% was presented as the temperature increased. While for the adsorbent synthesized using EG method, Hg0 removal efficiency first increased to the peak value of ca. 87% at 200 °C and then declined with the temperature increasing to 250 °C. A relatively strong oxidability facilitated the direct oxidation of the physically adsorbed Hg0 to HgO, which, to some extent, explained the higher Hg0 removal efficiency of the adsorbents synthesized using CP and HT methods at lower temperatures. Plentiful surface acid sites promoted the physisorption of Hg0, which was beneficial for the next Hg0 oxidation step and constituted an important reason for the elevated high-temperature Hg0 adsorption capability of the adsorbent prepared via EG method. During the Hg0 capture process, chemisorption dominated with Mn4+ acting as an active site to oxidize Hg0 and Ce4+ functioning as a promoter to accelerate the regeneration of Mn4+.

High-Temperature Solid Particle Erosion in a Melt-Infiltrated SiC/SiC Ceramic Matrix Composite

Abstract Ceramic matrix composites are an enabling propulsion material system that offer weight benefits over current Ni-based superalloys, and have higher temperature capabilities that can reduce cooling requirements. Incorporating ceramic matrix composites into the hot section of gas-turbine engines therefore leads to an increase in engine efficiency. While significant advancements have been made, challenges still remain for current and next-generation gas turbines; particularly when operating in dust laden or erosive environments. Solid particles entrained in the gas flow can impact engine hardware resulting in localized damage and material removal due to repeated, cumulative impacts. In this study, the erosion behavior of a melt-infiltrated (MI) silicon carbide fiber-reinforced silicon carbide (SiC/SiC) ceramic matrix composite is investigated at high temperature (1200 °C) in a simulated combustion environment using 150 μm alumina particles as erodent. Particle impact velocities ranged from 100 to 200 m/s and the angle of impingement varied from 30 to 90 deg. Erosion testing was also performed on α-SiC to elucidate similarities and differences in the erosion response of the composite compared to that of a monolithic ceramic. Scanning electron microscopy was used to study the posterosion damage morphology and the governing mechanisms of material removal.

Optimization of Al Heavy Wire Bonds Bond profile in WBG Power Module Design

Abstract Wide-Band Gap (WBG) semiconductors, such as SiC and GaN, have accelerated the ability to shrink the volumetric size and weight of power conversion systems by optimizing at the module level, due to their inherent high frequency, high temperature and high voltage capabilities. Power electronic module components, specifically flexible welded interconnects, behave like transmission lines at higher frequencies. Therefore, interconnects contribute to the power losses within the power module, and ultimately affect overall efficiency. Voltage and current overshoots and insertion/return losses and phenomena such as proximity and skin effect will also have a noticeable effect on the performance of the module as device switching is pushed into mid to high MHz range. Thus, to aid in design and development of advanced power modules this paper using FEA multiphysics solvers will firstly study the current carrying capacity and fusing time of different diameter Al heavy wire bonds interconnects. Then for a rated current, the multiple wire bond profile is considered to mitigate the negative effects from the fastest rising/fall edge of voltage and current switching high-frequency components. Characteristic impedance is then calculated using parasitic resistance and inductance for different wire bond profiles. The ultimate goal of the paper is to further the establishment of an evolution in thinking and designing when it comes to the WBG power electronic packaging practices and culture.

NiTiHf shape memory alloys as phase change thermal storage materials

Motivated by the recent advancements demonstrating the effectiveness of NiTi shape memory alloys (SMAs) as high figure of merit (FOM) phase change materials (PCMs) for thermal management and storage, NiTiHf SMAs were explored as candidate solid-solid PCMs with high temperature capability. Differential scanning calorimetry and Archimedes’ method were used to determine the transformation temperatures, thermal hysteresis, enthalpy of transformation, and density of several different NiTiHf SMAs with varying compositions. Ni50.3Ti29.7Hf20 (at. %) demonstrated a high transformation enthalpy of 32.5 J/g, a relatively low thermal hysteresis of 31°C and a thermal conductivity of 11.19 Wm−1K−1 in the austenite phase. In general, NiTiHf SMAs exhibited FOM values an order of magnitude higher than traditional PCMs and up to about 120 % higher than the FOM value measured in binary NiTi SMAs. The clear trends relating transformation temperatures, transformation enthalpy, and thermal hysteresis to composition presented here provide for tunability of NiTiHf SMAs to specific thermal energy storage applications through composition control. High FOM values combined with transformation temperatures surpassing 500°C allows NiTiHf alloys to populate previously empty regions of FOM vs. transformation temperature property space for high FOM PCMs.

Sialon-based Composites for Solar Receivers: An overview

Engineering non-oxide ceramics have recently been implied in many advanced applications based on their high temperature capability, outstanding strength, and low fabrication cost. As solar energy has become an economic trend and a clean source of energy; the utilization of ceramic materials as solar receivers in a solar thermal system has been widely considered. Various ceramic materials have shown their ability as heat absorber material due to their oxidation resistance, bending strength, thermal conductivity, and solar absorptance. Ceramics as Si3N4 and SiC can be valuable solar receiver materials; however, due to the high sintering temperature required for Si3N4 and the non-oxidizing nature of SiC; modification of these ceramics with AIN, oxide materials, and other additives is required. One of the highly promising trials that have proved its ability in a solar thermal system is modifying Si3N4 with Al2O3 and AIN that typically results in developing sialon-based ceramics. The latter materials have modified the flaws in many solar receiver ceramics as they have lower sinterability, lower fabrication cost, and easier densification compared to other solar receiver materials. The present work is an overview of the ceramic materials and composites applied as solar receivers, in addition to the characteristics required for the selected material sialons and the previous work achieved in this field.