The overview of ISO 185: 2020 Grey Cast Irons-Classification, the main contents of standard revision and typical applications were introduced.The main contents of the standard were described in ...detail, including the scope, material brand, tensile strength of cast sample, tensile strength of body sample, hardness, metallographic structure, sample preparation and retests.
Based on the first-principles method, the effects of pressure and temperature on the physical properties of Nbsub.2Bsub.3 and Tasub.2Bsub.3 were discussed. The approximate linear increase in B, G, ...and E with pressure was observed for Nbsub.2Bsub.3 and Tasub.2Bsub.3 with a minor difference for bulk modulus and similar values for shear and Young’s modulus. Nbsub.2Bsub.3 shows higher Vickers hardness and similar fracture toughness as compared with Tasub.2Bsub.3. An abnormal phenomenon of the simultaneous increase in hardness and B/G (σ) with the increased pressure was observed. The strong anisotropies of bulk, Young’s, and shear modulus were observed, and the differences of anisotropy between Nbsub.2Bsub.3 and Tasub.2Bsub.3 increased with pressure. At low temperatures, the α of Nbsub.2Bsub.3 is smaller than that of Tasub.2Bsub.3, but is larger than that of Tasub.2Bsub.3 at high temperatures. The Θ of Nbsub.2Bsub.3 are larger than those of Tasub.2Bsub.3 under the same conditions. The combination of relatively high Vickers hardness and fracture toughness is determined by the metallic bond and covalent bond. With the increased pressure, Nbsub.2Bsub.3 possesses the greater strength of B–B bonds than Tasub.2Bsub.3, which leads to its high hardness and Debye temperature.
Rare earth elements have been widely utilized in material manufacturing to enhance properties in various ways. In order to obtain the WC-10Co4Cr coating with uniform distribution of rare earths, ...CeOsub.2-modified powder was prepared by mixing 1 wt.% nano-sized CeOsub.2 during the initial ball-milling of the powder fabrication process. Bare and CeOsub.2-modified WC-10Co4Cr coatings were deposited via high velocity oxygen fuel spraying to investigate the impact of CeOsub.2 modification on the coating's microstructure, mechanical properties and abrasive wear performance. The results show that the addition of CeOsub.2 increased the interface energy, inhibiting the formation of the Cosub.3Wsub.3C phase during the powder sintering process, as well as the Wsub.2C phase and CoCr alloy during the high-velocity oxy-fuel (HVOF) process. This led to a significantly decreased porosity and higher concentration of undissolved Cr-rich areas. The microhardness and fracture toughness of the CeOsub.2-modified coating were 1230 HVsub.0.3 and 5.77 MPamsup.1/2, respectively. The abrasive wear resistance of the CeOsub.2-modified coating was only 70.9% of that of the unmodified coating. Due to the weak cohesive strength between WC and Cr, Cr-rich areas were preferentially removed, resulting in an increased wear rate in the CeOsub.2-modified coating.
Hardness is one of the critical physical characteristics of minerals and rocks, which indicates the resistance of the rock to penetration, scratch, or permanent deformation. As a basic concept, rock ...hardness has a significant role in rock mechanics and geological engineering and is an appropriate diagnostic tool for the classification of minerals and rocks. The main purpose of this study is to guide rock engineers to measure the rock hardness faster, easier, and more accurately using Leeb’s dynamic hardness test. Accordingly, this paper presents a new rock hardness classification system based on the Leeb dynamic and portable hardness testing method. It is a well-known method for its fast and straightforward procedure testing equipment. A set of 33 different rock types were collected and tested during this study. Next, in-depth microscopic mineralogical studies were performed to determine the precise Mohs hardness value. The Mohs hardness was considered the leading hardness benchmark during the experimental studies, and the Leeb hardness was adopted to classify based on this hardness. A series of laboratory studies and statistical analysis was performed to predict the Shore and Vickers hardness using Leeb hardness. Finally, based on the comparative studies, it is recommended to classify the rocks considering the Leeb hardness method in six different categories: extremely soft (1–250), soft (250–450), moderately soft (450–750), moderately hard (750–850), hard (850–920), and extremely hard (920–1000). The provided classification could be useful in a vast range of rock engineering applications, especially for feasibility studies of rock engineering projects and engineering geology.
Abstract
Reference materials for the Rockwell, Brinell and Vickers hardness scales are fundamental for the Brazilian industrial sector. Mechanical property Hardness is the most common mechanical test ...used for quality control of raw materials in finished products as well as in research and development of new products and materials. A description of the main findings of two studies and the revalidation of the last on the demand of hardness reference blocks in Brazil is presented. This paper shows national demand of hardness reference blocks could be supplied on a large scale by Inmetro´s Force Laboratory.
SK5 steel is the base material used for the preparation of the wrinkle scraper, whose service life strongly affects the working efficiency and economic benefits. In this work, WC-Cr3C2-Ni coating was ...deposited on the SK5 steel substrate by using High-velocity air fuel spray (HVAF) and Laser cladding (LC) processes respectively, named HVAF-WC coating and LC-WC coating. The microstructure and wear resistance of both coatings were analyzed, and were compared with the substrate sample. Results showed that the coatings were adhesive well onto the substrate. More WC with fine crystals is retained in HVAF-WC coating due to low flame flow temperature, while WC of LC-WC coating is characterized by columnar crystals. The wear rate of HVAF-WC and LC-WC coating was 4.00 × 10sup.−7 mmsup.3/(N*m) and 3.47 × 10sup.−6 mmsup.3/(N*m), respectively, which was two and one orders of magnitude lower than SK5 steel with 3.54 × 10sup.−5 mmsup.3/Nm. HVAF-WC coating exhibited the best wear resistance because of significant fine grain strengthening, which wear mechanism is mainly dominated by abrasive wear. Thus, it was thought that HVAF-WC coating is more effective ways to improve the wear resistance of SK5 steel, comparing with LC-WC coating.
Chemical hardness is considered to be a useful theoretical descriptor in many experimental and theoretical studies and this concept has several important applications in chemistry. In this study, an ...equation for atomic hardness is proposed. Following the equation for atomic hardness which is based on charges, ionisation energies and electron affinities of atoms, a new equation is obtained for the calculation of the chemical hardness of groups and molecules using the atomic hardness equation and the principle of chemical hardness equalisation. Molecular chemical hardness may be calculated using α and β parameters of atoms in a molecule or group through the use of the obtained molecular hardness equation. Furthermore, the advantage of this equation over other equations in the literature is that using this equation the chemical hardness of the charged groups and molecules can also be calculated. Besides, the relationship between molecular hardness and charge of molecule is examined using the results obtained from the new molecular hardness equation, and the partial charges of atoms in molecules are calculated with the help of derived equations.
Prediction of physical and mechanical properties of rock materials using rebound-based hardness test methods is widely preferred in many fields of engineering and in the characterization of rock ...materials, because they are non-destructive, practical, and economical. In this study, 40 types of rocks with magmatic, metamorphic, and sedimentary origins, represented by travertine, limestone, marble, dolomite, granite, syenite, dunite, andesite, schist, gabbro, tuff, and ignimbrite were selected. First, dry unit weight (
γ
d
), open porosity (
n
o
), water absorption by weight (
W
AW
), wide wheel abrasion (
W
A
), and uniaxial compressive strength values were determined. After that, Shore C-2 scleroscope (HS
C
), L-type Schmidt hammer (HS
L
), and Leeb (HL
D
) rebound-based hardness tests were carried out on all samples, and then, hardness values by three methods were compared with the obtained parameters. The Leeb hardness test, which is more recent and innovative than the Shore and Schmidt hardness tests, was initially developed for metallic materials. However, the method has become increasingly popular in the determination of hardness of rock materials in laboratory as well as in field. In this study, the Leeb hardness test was found to be more useful due to its quick and precise measurement capabilities compared to Shore and Schmidt hardness tests. The results of the study reveal that the prediction of physical and mechanical properties of rocks can more precisely be determined by the HL
D
method than the HS
L
and HS
C
methods using the proposed equations.
PDF
