CARBON-CARBON COMPOSITE MATERIALS WITH 3D REINFORCEMENT FUNCTIONAL PROPERTIES DEPENDENCES RESEARCH

Thermal expansion is an important design parameter of materials, which should be taken into account when developing, producing and using products. To control this significant characteristic of new materials, it is necessary to develop equipment, methods and measurement procedures that take into account the novelty of the specific behavior of these materials. The production of specially shaped samples is the main limitation in thermal expansion measurements. This primarily applies to new materials (heterogeneous, composite, poorly processed) developed for special tasks. These factors necessitated the development of a method for measuring the temperature coefficient of linear expansion of products and materials with arbitrary sample shapes, which was not available in previous implementations of interferometric methods. An interference speckle dilatometer SD was developed for measuring samples with irregular shape in the temperature range from 200 to 400 K. When creating the speckle dilatometer SD, the speckle interferometry method was implemented to measure the elongation of samples with an irregular surface with nanometer sensitivity. Since this device has no analogues, a study was conducted on the uncertainty components arising when measuring the thermal coefficient of linear expansion of materials on this device. The analysis of the uncertainty components of the measurement of the thermal coefficient of linear expansion of materials on the speckle dilatometer SD was carried out. An experimental determination of the measurement uncertainty of the thermal coefficient of linear expansion of TCLE measures of arbitrary shaped samples was obtained using the SD speckle dilatometer. After research and initial certification, the developed measurement instrument was approved and included in the State Secondary Standard of the unit of thermal coefficient of linear expansion of solids in the range of values from 0.05 · 10–6 to 100.0 · 10–6 K–1 in the range of temperature values from 90 to 1,900 K.

Relevance. Coatings based on bioactive glass are widely used in maxillofacial and orthopedic implantology due to their ability to osseointegration, degradation control and bone compatibility. At the same time, when implants are operated in loaded areas, glass coatings experience mechanical loads, thermal fluctuations and the effects of an aggressive biological environment, which places high demands on their crack resistance, adhesion and thermo-mechanical stability. Objective. To carry out a comparative evaluation of the performance characteristics of the new bioactive coating for the dental implant FAR-5X and its analogue, aimed at identifying potential advantages in mechanical stability and compatibility with the titanium base. Materials and methods. This study presents a comparative analysis of the mechanical properties of two glass–ceramic composite coatings, FAR-5X and FAR-5.3/E, designed for application on titanium implants. The analysis focused on key mechanical parameters, including the coefficient of thermal linear expansion, Vickers microhardness, fracture toughness, Young’s modulus, and adhesion strength. All measurements were performed on seven samples of each coating type using standard micro-mechanical testing methods. Statistical processing was conducted using one-way ANOVA and Tukey's post-hoc test. Results. The developed glass composite coating FAR-5X demonstrates a set of high-performance characteristics due to its nanostructured morphology obtained through optimized thermal treatment. This approach promotes a homogeneous distribution of the crystalline phase within the amorphous matrix, enhancing the material’s mechanical integrity. The results revealed a statistically significant higher coefficient of thermal linear expansion value in the FAR-5X coating compared to FAR-5.3/E (p < 0.05), indicating improved thermomechanical compatibility with the titanium substrate. A statistically significant difference between the coatings was found only in the coefficient of linear thermal expansion, indicating better thermal compatibility of FAR-5X with the titanium base. No significant differences were observed in microhardness, fracture resistance, elastic modulus, or adhesion strength, confirming comparable mechanical integrity between the coatings. Conclusion. The findings suggest that the newly developed FAR-5X coating offers advantageous thermal expansion behavior while maintaining the necessary mechanical robustness, supporting its potential application as a bioactive coating in orthopedic and dental implant systems.

The corrugated layer structure bismuth has been successfully tailored into negative thermal expansion along c axis by size effect. Pair distribution function and extended X-ray absorption fine structure are combined to reveal the local structural distortion for nanosized bismuth. The comprehensive method to identify the local structure of nanomaterials can benefit the regulating and controlling of thermal expansion in nanodivices.

Effective thermal expansion of heterogeneous materials with application to low temperature environments

The mean coefficient of linear thermal expansion is used to define a new “instantaneous coefficient of linear thermal expansion” (ILTE) which is proved to be independent of reference temperatures required to define mean values. Hence it can be considered a true material property. The new ILTE provides a common reference to compare thermal expansion data of different materials. This instantaneous coefficient is different from the instantaneous value defined by ASTM standards. Values of the new coefficient are compared with the widely used mean coefficient values. Accuracy of calculations using the new ILTE is demonstrated using the mean coefficient data of two materials.

The thermomechanical analyzer (TMA) is eminently suitable for the measurement of the thermal expansion coefficient of rubbers, provided the equipment is calibrated with materials of similar expansion coefficient. FKM or other thermally stable and amorphous polymers (of independently determined thermal expansion characteristics) can be used as calibration standards. The relative simplicity and precision of the TMA method for the determination of the coefficient of isotropic linear expansion, and hence, of volumetric expansion of rubbers, makes this important thermodynamic parameter easily accessible experimentally. Because of the frequently observed anisotropy of molded elastomeric compounds, measurements in all three dimensions are required to define linear, isotropic expansion and shrinkage which, to an excellent approximation, are represented by arithmetic averages of the three unidirectional values. Good agreement has been found between the average (isotropic) shrinkage determined experimentally and that calculated from the average (isotropic) coefficient of linear thermal expansion, α. The effect of fillers, such as carbon black, on α is additive. This makes it possible to predict α and shrinkage of all filled compounds from a single value of α of the unfilled rubber. The linear thermal expansion coefficients of the tested rubbers (FKM, NBR, EPDM) increase linearly with temperature, the increase being generally stronger for FKM than for the other elastomers. The appreciably higher mold shrinkage of FKM relative to NBR is directly due to the higher α of FKM for comparable levels of fillers. This must be kept in mind when expedience dictates the use of the same molds for FKM and NBR compounds.

The results of dilatometric studies of thermal coefficient of linear expansion of dysprosium in the temperature range 110-1950 K are presented. The measurements were performed with an accuracy of (1.5-2.0)·10-7 K-1. The approximation dependences of thermal coefficient of linear expansion were obtained. The reference tables of dysprosium thermal properties for the range 110-1950 K of solid and liquid states were constructed using the previous results obtained by the gamma method. The character of thermal coefficient of linear expansion changes in the area of the Neel point has been established. Its critical exponents and the critical amplitudes have been determined. It is shown that both above and below the Neel temperature, the experimental data cannot be processed with a single scaling equation. A comparison with the published data has been performed.

Because of the lack of data on the thermal expansion of natural solid wood and many wood products, such as plywood, impreg, compreg, and many others, studies were conducted at the Forest Products Laboratory in an effort to obtain such data. The coefficients of linear thermal expansion, called α were measured on a wide variety of wood materials in three structural directions. General formulas were developed which permit calculation of the coefficients of linear thermal expansion in any grain direction of the specimen from the original and final specific gravities, the percentage by weight of resin and glue present, the percentage of cross-banding, and the slope of grain relative to any three axes of reference.

Influence of the structural state and crystallographic texture of Zr-2.5% Nb alloy samples on the anisotropy of their thermal expansion

Dispersion-strengthened composite materials belong to the group of promising structural materials characterized by a diverse combination of properties. The work presents examples of the creation and heat treatment of composite materials based on aluminum alloys, strengthened by a dispersed phase of titanium carbide, and characterized by high hardness, elastic modulus and good wettability by the melt. The most accessible, inexpensive and effective way to obtain them is self-propagating high-temperature synthesis (SHS).The work shows the possibility of obtaining new aluminum matrix composite materials based on industrial aluminum alloys AM4.5Kd and AK10M2N by reinforcing them with 10 wt.% highly dispersed titanium carbide or AM4.5Kd–5.95 vol.% TiC and AK10M2N–5.78 vol.% TiC. The reinforcing phase is formed in alloy melts using the technology of SHS from the initial elemental components—titanium powder and carbon black. Using the obtained samples, an assessment was made of the uniformity of the ceramic phase distribution over the volume of the matrix alloys, which amounted to 0.15 and 0.12 for the samples AM4.5Kd–10%TiC and AK10M2N–10%TiC, respectively, which constitutes a high degree of uniformity.An assessment was made of physical properties such as porosity, density, electrical conductivity, as well as the coefficient of thermal linear expansion. Analysis of the data allows us to say that the final composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC have a slightly higher density (↑~4%) than the matrix alloys, due to the presence of a ceramic phase, low porosity values (~1%), lower TCLE (↓~6%) than matrix alloys and low electrical conductivity (~25% IACS). This article also presents data on the values of the mechanical properties of composite materials AM4.5Kd–10%TiC and AK10M2N–10%TiC. It has been shown that reinforcement with a ceramic phase contributes to a significant increase in hardness by 15 and 42 HB, as well as higher values of the compressive yield strength by 31 and 17 MPa, respectively, while maintaining a high level of relative deformation. The results obtained allow us to conclude that the developed composite materials can be recommended for products used under conditions of elevated temperatures and significant wear.

A new technique for measuring Young's modulus of an ultra-thin film, with a thickness in the range of about 10 nm, was developed by combining an optical lever technique for measuring the residual stress and X-ray diffraction for measuring the strain in the film. The new technique was applied to analyze the mechanical properties of Ga-doped ZnO (GZO) films, that have become the focus of significant attention as a substitute material for indium-tin-oxide transparent electrodes. Young's modulus of the as-deposited GZO films decreased with thickness; the values for 30 nm and 500 nm thick films were 205 GPa and 117 GPa, respectively. The coefficient of linear thermal expansion of the GZO films was measured using the new technique in combination within-situresidual stress measurement during heat-cycle testing. GZO films with 30–100 nm thickness had a coefficient of linear thermal expansion in the range of 4.3 × 10−6– 5.6 × 10−6 °C−1.

Invar alloys – a group of magnetically ordered alloys with a very low thermal linear expansion coefficient. The small values of the thermal coefficient of linear expansion are due to the fact that the usual (‘Debye’) thermal expansion is compensated for in these alloys by a reduction in size associated with large spontaneous magnetostriction. The difference between Invars and ordinary magnetically ordered alloys, in which thermal expansion anomalies are manifested in a narrow region near the Curie (Neel) point, lies in the fact that in Invars these anomalies are observed in the entire temperature range of the existence of magnetic ordering. Some exotic behaviors of invar have not yet been fully understood. Therefore, the problem of studying the anomalies of physical properties in such alloys is urgent. Annealing conditions of the Invar and dimensional effects of cast foundry state Invar alloy Fe-Ni (38) – C (2.5) specimens have been investigated in this study.

The coefficient of thermal linear expansion (CTE) of a superplastically elongated 3Y-TZP (3 mol.% yttria stabilized tetragonal zirconia polycrystal) was investigated. The experiments were conducted by using a push-rod dilatometer at a wide temperature range from 300K to 1473K. The experimental results indicated that CTE increased from 11.0×(10)^<-6>K^<-1> to 12.0×(10)^<-6>K^<-1> with increasing temperatures from 773K to 1200K and then showed temperature independence. Also, deformation-induced change in microstructures such as volume of cavitations fraction, the average grain size and grain aspect ration has little effect on CTE within to present experimental range.

High temperature thermal expansion of BaAl2Si2O8, CaAl2Si2O8, and Ca2Al2SiO7 studied by high-temperature X-ray diffraction (HT-XRD)

High density polyethylene (HDPE) is a thermoplastic polymer which is classified as one of the highly consumed types of plastics. One major advantage of thermoplastic materials is their ability of recycling and reprocessing which will bring considerable economic and environmental benefits. The present paper, therefore, endeavors to explore the practical possibility of using recycled HDPE hollow section as a replacement of virgin HDPE made by the extrusion process. The main focus of the study was to evaluate the mechanical performance of the recycled HDPE and compare the results with virgin or non-recycled HDPE. The modulus of elasticity, tensile yield and ultimate strength, compressive yield and ultimate strength, flexural yield and ultimate strength and the coefficient of thermal expansion were the main parameters to be checked against the respective mechanical properties. Thus, pursuant to the results, it was found out that the modulus of elasticity and the tensile yield strength are lower in recycled HDPE compared to the non-recycled HDPE. However, there is no significant difference between the recycled and non-recycled HDPE for the tensile ultimate strength, compressive yield strength and compressive ultimate strength. The flexural yield strength and flexural ultimate strength properties of the recycled HDPE proved to be superior to those of the non-recycled HDPE. The coefficient of linear thermal expansion of the recycled HDPE sample was 130 μm/(m.°C) and that for the non-recycled HDPE was 142 μm/(m.°C).