Thermal Expansion Coefficients Of Materials Research Articles

Influence of residual stress on the high-temperature tribological performance of nickel-based superalloy

This study introduces a method for generating residual compressive stress by utilizing differences in thermal expansion coefficients of materials. A corresponding experimental device has been developed. Using this method, experiments were conducted to investigate the effects of residual compressive stress on the tribological properties of the nickel-based superalloy Ni16Cr13Co4Mo. The results indicate that residual stress significantly affects the friction behavior and wear resistance of the superalloy. The stabilization time of the friction coefficient as well as the wear rate reaches a minimum under moderate residual compressive stresses. Moderate residual compressive stress can facilitate the formation of a tribo-oxide layer and enhance its bonding strength with the substrate, thereby shortening the time for stabilization of the friction coefficient and reducing the wear rate. Finite element simulation of static ball-on-disc contact model also shows that residual stress alters the internal stress distribution inside the alloy, and changes its yield and plastic behavior. Under moderate residual compressive stress, a reduction in maximum von Mises stress can be achieved, which is consistent with the variation rule of friction coefficient and wear rate in the tests.

Effect of laser energy density on cracking susceptibility and wear resistance of laser-clad tribaloy T-800 coatings on DD5 single-crystal alloys

In order to enhance the wear resistance of DD5 single-crystal alloys, Tribaloy T-800 wear-resistant coatings were prepared on their surfaces using laser-cladding technology. This study examines the effect of laser energy density on the cracking susceptibility and wear resistance of laser-clad Tribaloy T-800 coatings on DD5 single-crystal alloys. Three distinct laser energy densities (η1=33 J/mm², η2=50 J/mm², η3=60 J/mm²) were applied to create the coatings. The results show that the microstructures of the T-800 laser-clad coatings mainly consist of primary, coarsened, and spheroidized Laves phases, as well as Co-based solid solution and eutectic structures. The phases include Co3Mo2Si phase (Laves phase) and face-centered cubic Co-based solid solution. However, increasing laser energy density enhanced elemental diffusion at the heterogeneous joining interface of the DD5 substrate/T-800 coating, leading to higher Ni content in the coating. This resulted in a reduction in the tendency and content of Mo-rich Laves phase formation respective contents of 53.2 %, 49.2 %, and 47.5 %. Moreover, the decrease in the difference between laser cladding temperature and initial temperature, ∆T, led to reduced thermal stress at the interface, σ, contributing to a decrease in cracking susceptibility (a), with corresponding values of 0.16184, 0.00034, and 0.00022. Thermal expansion coefficients of materials in the cracked region near the interface, measured according to the CALPHAD method, Jmatpro software, and average EDS elemental content data at the crack edge, surpassed those of the corresponding DD5 substrate. Consequently, cracks in the coatings originated from stretching at the interface, with paths tending to cross Laves phase particles in a cleavage mode. The average microhardness of the coatings decreased due to reduced Laves phase content, with values of 783.4 HV0.5, 741.7 HV0.5, and 708.2 HV0.5, respectively, while the fatigue wear of T-800 coatings increased due to exacerbated wear damage from cracking defects. Specifically, average COFs were 0.659, 0.583, and 0.506, with corresponding mass losses of 7.1 mg, 3.4 mg, and 2.9 mg, respectively. The wear mechanisms observed encompassed fatigue wear, abrasive wear, and oxidative wear.

Laser Processing of Polyimide and Molybdenum Substrates for Extreme Environment Electronics

A desire in today’s electronic packaging technologies is to create more dense electronic packaging schemes. One method to achieve more dense electronic package integration is to use three-dimensional interconnects to minimize interconnect physical dimensions. Three-dimensional interconnect technologies, such as interposers, require a method of connecting electronics to electronic packages vertically. Thru silicon vias are a widely studied and explored vertical interconnect technology used in a variety of electronic packaging applications. Though silicon has high material hardness, the brittle nature of silicon substrates is a concern for robustness and reliability. These concerns only increase when the desired interconnect application is in extreme environments, such as cryogenic temperatures. A potential alternative to silicon in thru-via applications in extreme environments is molybdenum. Molybdenum is a commonly used material in many applications, such as automotive and aerospace, and has high material strength. Molybdenum is also a low coefficient of thermal expansion material, comparable to silicon, which in combination with high material strength lends to high reliability at extreme temperatures. A challenge of working with refractory metals such as molybdenum is that conventional CNC machining techniques require the use of machining coolants that may not be compatible with fabricated electronics and/or processes can become costly due to tool wear and the need for specialized equipment. Additionally, using molybdenum as a thru-via substrate requires the need for an electrically insulated layer, such as polyimide, within drilled molybdenum thru-holes to prevent the molybdenum substrate from shorting via connections. One potential solution to the above challenges is developing laser processing techniques to cut and drill molybdenum and polyimide. Laser processing is becoming a preferred method for inexpensive prototyping with high resolution and design versatility. This work seeks to meet the challenges described by developing laser cutting and drilling techniques for both molybdenum and polyimide for the use in cryogenic applications. This work will describe two laser processing configurations utilizing two different lasers to laser machine molybdenum and polyimide. This work will first describe the process strategies of laser cutting and drilling molybdenum as a stand-alone substrate. Aspects of laser processing on molybdenum, such as pattern repetitions and scanning speeds, will be described. Process parameter variations will be compared directly and evaluated. Additionally, post-laser processing steps, such as abrasive blasting, will be described and discussed. Next, the fabrication steps to achieve an insulating layer of polyimide in laser drilled holes as well as on each surface of the molybdenum will be detailed. Once polyimide has been cured, laser processing parameters to realize thru-holes in the polyimide-filled molybdenum drills will be presented. Adhesion of polyimide on the molybdenum substrate will be verified and demonstrated through the use of confocal scanning acoustic microscopy before and after polyimide laser processing. Cryogenic performance will be verified by completing confocal scanning acoustic microscopy after submersion in liquid nitrogen (~77 K) and compared with the pre-submersion microscopy images. Processes detailed in this work will open opportunities for future development of molybdenum-based interconnect structures for use in cryogenic applications. Acknowledgement We thank the Alabama Micro/Nano Science and Technology Center (AMNSTC) for providing access to fabrication and characterization facilities used in this work.

Elastemp — A workflow to compute the quasi-harmonic temperature dependent elastic constants of materials

Elastic constants characterize the stiffness of a material. A linear relationship between the stress and strain tensors in the limit of infinitesimal deformation is used to define and compute the elastic constants. Typically, this is computed at zero temperature by deforming the simulation box in one of the six directions and computing the stress tensor. Calculating elastic constants at finite temperature is more challenging owing to large fluctuations and thermal noise. Here, we introduce a semi-automated workflow — Elastemp, to obtain the quasi-harmonic elastic constants of materials as a function of temperature. The workflow integrates with electronic structure packages such as VASP and PHONOPY to get the quasi-harmonic energies. The workflow is capable of estimating the zero temperature elastic constants, thermal expansion coefficients of materials and temperature dependent elastic constants. The predictions for a set of representative test cases with different crystal symmetries (Al, Diamond, Titanium nitride (TiN) and α-Ti) are compared with experiments and used to demonstrate the efficacy of our workflow.

Thermal expansion and boundary excess free volume of electroformed nanocrystalline Ni-Co from dilatometer and digital caliper measurements

The coefficient of thermal expansion (CTE) as measured by dilatometry of electroformed nanocrystalline Ni-32at%Co macro-defect free sheet metal up to 500 °C can be separated into three regions. Below 185 °C, the nanocrystalline material's CTE is similar to its polycrystalline counterpart. Between 185 and 310 °C, the CTE of the nanocrystalline material plateaus, then drops at temperatures above 310 °C due to volume shrinkage induced by different grain growth stages. The grain boundary excess volume (BEV) was determined to be between 0.20–0.24 nm. In addition, it is shown that simple digital caliper measurements are a reliable technique to estimate BEV for specimens with grain boundaries being the main defect.

Frequency-domain probe beam deflection method for measurement of thermal conductivity of materials on micron length scale.

Time-domain thermoreflectance and frequency-domain thermoreflectance (FDTR) have been widely used for non-contact measurement of anisotropic thermal conductivity of materials with high spatial resolution. However, the requirement of a high thermoreflectance coefficient restricts the choice of metal coating and laser wavelength. The accuracy of the measurement is often limited by the high sensitivity to the radii of the laser beams. We describe an alternative frequency-domain pump-probe technique based on probe beam deflection. The beam deflection is primarily caused by thermoelastic deformation of the sample surface, with a magnitude determined by the thermal expansion coefficient of the bulk material to measure. We derive an analytical solution to the coupled elasticity and heat diffusion equations for periodic heating of a multilayer sample with anisotropic elastic constants, thermal conductivity, and thermal expansion coefficients. In most cases, a simplified model can reliably describe the frequency dependence of the beam deflection signal without knowledge of the elastic constants and thermal expansion coefficients of the material. The magnitude of the probe beam deflection signal is larger than the maximum magnitude achievable by thermoreflectance detection of surface temperatures if the thermal expansion coefficient is greater than 5 × 10-6K-1. The uncertainty propagated from laser beam radii is smaller than that in FDTR when using a large beam offset. We find a nearly perfect matching of the measured signal and model prediction, and measure thermal conductivities within 6% of accepted values for materials spanning the range of polymers to gold, 0.1-300 W/(m K).

Investigation of Temperature-Dependent Magnetic Properties and Coefficient of Thermal Expansion in Invar Alloys.

Invar Fe–Ni alloy is a prominent Ni steel alloy with a low coefficient of thermal expansion around room temperature. We investigate the correlation between magnetic properties and thermal expansion in cold-drawn Fe–36Ni wires with different heat treatment conditions, where the annealing parameters with furnace cooling (cooling from the annealing temperature of 300, 400, 500, 600, 700, 800, 900, and 1000 °C) are used. The variation trend of magnetic properties is consistent with that of thermal expansion for all samples, where the maximum appears at 600 °C -treated sample and 400 °C shows the minimum. The domain size and the area of domain walls determine the total energy of the domain wall, and the total energy directly determines the size of magnetostriction, which is closely related to the coefficient of thermal expansion. Also, the differential thermal analysis (DTA) shows endothermic and exothermic reactions represent crystalline transitions, which could possibly cause the abrupt change of magnetic properties and thermal expansion coefficient of materials. The results indicate that there is a certain relation between thermal expansion and magnetic properties. Besides the fundamental significance, our work provides an Invar alloy with a low coefficient of thermal expansion for practical use.

X-ray Diffraction Techniques for Mineral Characterization: A Review for Engineers of the Fundamentals, Applications, and Research Directions

X-ray diffraction (XRD) is an important and widely used material characterization technique. With the recent development in material science technology and understanding, various new materials are being developed, which requires upgrading the existing analytical techniques such that emerging intricate problems can be solved. Although XRD is a well-established non-destructive technique, it still requires further improvements in its characterization capabilities, especially when dealing with complex mineral structures. The present review conducts comprehensive discussions on atomic crystal structure, XRD principle, its applications, uncertainty during XRD analysis, and required safety precautions. The future research directions, especially the use of artificial intelligence and machine learning tools, for improving the effectiveness and accuracy of the XRD technique, are discussed for mineral characterization. The topics covered include how XRD patterns can be utilized for a thorough understanding of the crystalline structure, size, and orientation, dislocation density, phase identification, quantification, and transformation, information about lattice parameters, residual stress, and strain, and thermal expansion coefficient of materials. All these important discussions on XRD analysis for mineral characterization are compiled in this comprehensive review, so that it can benefit specialists and engineers in the chemical, mining, iron, metallurgy, and steel industries.

Tuning Epoxy Thermomechanics via Thermal Isomerization: A Route to Negative Coefficient of Thermal Expansion Materials.

Fine control over the thermal expansion and contraction behavior of polymer materials is challenging. Most polymers have large coefficients of thermal expansion (CTEs), which preclude long performance lifetimes of composite materials. Herein, we report the design and synthesis of epoxy thermosets with low CTE values below their Tg and large contraction behavior above Tg by incorporating thermally contractile dibenzocyclooctane (DBCO) motifs within the thermoset network. This atypical thermomechanical behavior was rationalized in terms of a twist-boat to chair conformational equilibrium of the DBCO linkages. We anticipate these findings to be generally useful in the preparation of materials with designed CTE values.

Studying the applicability of amorphous metal alloys as interface material for power electronics packaging

All-atom Molecular Dynamics simulations were used to study the coefficient of thermal expansion (CTE) in Cu/Zr amorphous alloys with various compositions. We explored the possibility of using these alloys as bonding interface material between ceramics chips and copper leads in power electronics and microelectronic packaging applications with an objective of reducing CTE mismatch at the bonding interface. It was expected that with the appropriate design of reduced CTE mismatch at the interface, the Cu/Zr bonding layer could withstand larger thermal loads and significantly extend device life compared to the devices that currently implement directly bonded copper (DBC) approach. The non-monotonic increase of material CTE with copper content in the alloy was analyzed and explained using new tessellation algorithm that is focused on the configuration of close contacts between the neighboring atoms. The modeling using Turner equation shows that the “leveling” of CTE dependence in the mid-composition range is due to the contribution from non-tetrahedral polyhedra and would be expected for any binary glass system. Contrary to that, the “dip” at Cu-rich compositions is caused by the nature of the metallic bonding in the alloy, and is specific to Cu-Zr glass.

Highly-doped SiC resonator with ultra-large tuning frequency range by Joule heating effect

Tuning the natural frequency of a resonator is an innovative approach for the implementation of mechanical resonators in a broad range of fields such as timing applications, filters or sensors. The conventional electrothermal technique is not favorable towards large tuning range because of its reliance on metallic heating elements. The use of metallic heaters could limit the tuning capability due to the mismatch in thermal expansion coefficients of materials forming the resonator. To solve this drawback, herein, the design, fabrication, and testing of a highly-doped SiC bridge resonator that excludes the use of metallic material as a heating element has been proposed. Instead, free-standing SiC structure functions as the mechanical resonant component as well as the heating element. Through the use of the Joule heating effect, a frequency tuning capability of almost ∆f/fo ≈ 80% has been demonstrated. The proposed device also exhibited a wide operating frequency range from 72.3 kHz to 14.5 kHz. Our SiC device enables the development of highly sensitive resonant-based sensors, especially in harsh environments.

Ultra‐low thermal expansion behavior of spark plasma sintered Sn‐doped ZrMo2O8

AbstractSn‐doped ZrMo2O8 exhibits a coefficient of thermal expansion that is tunable based on the amount of Sn present in the Zr lattice sites. The current study focuses on the facile sintering of this material using spark plasma sintering (SPS) process. Powder particles of the material were produced by co‐precipitation, and the formation of the desired cubic phase was confirmed using X‐ray diffraction. The powder particles were sintered using SPS at different temperatures to identify the optimum sintering conditions. The extremely high rate of heating during SPS process enables complete sintering while retarding the decomposition reactions. It was noticed that attaining dense phase pure samples is strongly dependent on the sintering conditions. The results from the dilatometry carried out on the sintered pellets resulted in ultra‐low thermal expansion coefficients in the order of 10−7/°C for the samples sintered at 500°C. Comparisons with other commercially available low coefficient of thermal expansion materials highlight the advantage of the current work.

Analysis of Data on Zero and Negative Thermal Expansion Coefficients of Materials

Many specific features and anomalies of the properties of water at low temperatures and negative pressures or hydrogen and nitrogen at megabar pressures and high temperatures are related to zero and negative coefficients of thermal expansion. A review of numerous examples of manifestation of these features for various materials in different states is presented. A set of data and methods for the analysis of negative thermal expansion coefficients is singled out for an independent line of research.

Thermal stress analysis by finite elements of a metal-ceramic dental bridge during the cooling phase of a glaze treatment

In the present paper, a computational finite element analysis (FEA) was developed by using the COMSOL Multiphysics® software to evaluate the thermal accumulated stress on a 3-unit dental ceramic pressed over metal (POM) bridge, at different cooling rates during the glaze treatment. The cooling rates are related to the free opening of the furnace at 800 °C (extreme case) and the restricted opening when the restoration reaches 450 °C (slow case). The thermal expansion coefficients of the materials and the glass transition point of the ceramic were measured experimentally using a dilatometer test. The FEA was performed based on the ceramic temperature profile, which was determined experimentally by using thermocouples type K. When the dental ceramic reaches its transition temperature (Tg) at 510 °C, maximum principal stress at the grooves from the occlusal surface of the pontic are reported as 140 MPa for the slow and 400 MPa for the fast cooling rate. Additionally, it is demonstrated that stresses can be reduced by using low Young's modulus metals and with small differences in the material's thermal expansion coefficient (CTE).

Determination of thermal expansion coefficients in shocked compounds

Differences in volumes of solid compounds compressed by the static (cold) and shock-wave (adiabatic) methods are caused by the enhanced temperatures in the last case that allows the determination of thermal expansion coefficients of materials under pressures. Thermodynamic consideration of the thermal behavior in compressed solids shows that, usually, positive ▵V under ambient conditions implies negative ▵V under high pressure, and vice versa. The changing sign of ▵V is not due to structural transformations.

Analysis of the technology to manufacture a high-temperature microstrip superconductive device for the electromagnetic protection of receivers

Technological features of the process of manufacturing a high-speed high-temperature superconducting microstrip protective device which can reduce in a picosecond period (the time of switching or operation speed) the incoming power from the antenna-feeder path and the power passing through it to a level safe for sensitive semiconductor elements of the receiver (preventing current destruction of p-n junction). The study enables determination of the features and conditions for the use of modern technological methods for creating a superconducting microstrip protective device taking into account influence of the substrate material, superconductor and contacts and the method of their connection on the switching properties of superconducting films of the proposed protective device. The switching properties of superconducting films include speed of phase transition of a film from a superconducting to a nonconducting state. To determine degree of material influence on switching properties, it was proposed to use the following: lattice parameter, thermal expansion coefficient of materials, degree of interaction of molecular structures of the contacting surfaces, probability of local defects on the surface (nonconducting zones). The study outlines basic conditions (methods of film deposition, applying a certain superconducting film (YBCO) on the chosen substrate) which should be met in order to create an operable protective device. The study results make it possible to assess the degree of influence of contact materials and the method of deposition (of both film on the substrate and contacts on the film) on microstructure and switching properties of the superconducting protective device. Such results can be used in synthesis of high-temperature superconducting devices for protecting receiver elements from current destruction of their p–n junctions

Thermal expansion coefficient measured by single slit diffraction

The determination of thermal expansion coefficient of materials is a representative experiment in thermal experiments.With the application of modern computer methods to experiments,When measuring the material’s thermal expansion coefficient, the thermal expansion coefficient of the material is calculated by measuring the distance between the diffraction stripes. However, there are significant errors in conventional methods, because of the limitation of the observation of diffraction stripes through human eyes. By improving the receiving device, the diffraction fringe is monitored in real time by using a CCD data acquisition system, which is not only easy to operate, but also reduces the coefficient of thermal expansion of the calculated material by computer programming, which is close to the real value.

Testing Contraction and Thermal Expansion Coefficient of Construction and Moulding Polymer Composites

Abstract The paper presents results of systematic tests of contraction and thermal expansion coefficients of materials based on polymer composites. The information on the above material properties is essential both at the design stage and during the use of finished products. Components for the samples were selected in such a way as to represent typical materials used for production of construction and moulding elements. The performed tests made it possible to monitor the analysed parameters at different stages of the technological process.

Enhanced thermal expansion by micro-displacement amplifying mechanical metamaterial

ABSTRACTIt is important to achieve materials with large coefficient of thermal expansion in science and engineering applications. In this paper, we propose an experimentally-validated metamaterial approach to amplify the thermal expansion of materials based on the guiding principles of flexible hinges and displacement amplification mechanism. The thermal expansion property of the designed metamaterial is demonstrated by simulation and experiment with a temperature increase of 245 K for the two-dimensional sample. Both experimental and simulation results display amplified thermal expansion property of the metamaterial. The effective coefficient of thermal expansion of the metamaterials is demonstrated to be dependent on the size parameters of the structure, which means by appropriately tailoring these parameters, the thermal expansion of materials could be amplified with different amplification factor. This work provides an important method to control the thermal expansion coefficient of materials and could be applied in various industry domain.

Heterogeneously Integrated Membrane Lasers on Si Substrate for Low Operating Energy Optical Links

High demand exists for low operating energy optical links that use wavelength division multiplexing technologies in datacenter networks. Thus, we fabricate a directly modulated membrane distributed-reflector laser with low operating energy on a thermally oxidized silicon (Si) substrate. Because we use epitaxial growth to bury an active region on a directly bonded InP-based membrane, it needs to be kept within a critical thickness, which is related to the growth temperature and the thermal expansion coefficients of materials. In previous studies, we used 250-nm-thick structures, causing relatively large series resistance that limited device performance on such aspects as energy cost and output power. In this study, we increase the III–V membrane thickness to 350 nm, which is close to the calculated critical thicknesses. We achieve the same high crystal quality of multiquantum-wells found in our previous studies. The fabricated laser shows a differential resistance of 72 Ω and thermal resistance of 982 K/W. Thanks to a reduction in bias voltage, the laser can be directly modulated at 25.8 Gbit/s with an energy cost of 97 fJ/bit. In addition, due to a reduction in heat generation, direct modulation with a 50-Gbit/s non return to zero signal is demonstrated by increasing bias current up to 10 mA.