Large sized SiC based wear, corrosion and thermal shock resistant ceramics produced by thixotropic casting technology

Chromium oxide coatings are chemically inert, have high mechanical strength, hardness and good optical characteristics; therefore, they have been widely used in many applications including corrosion protection, wear resistance, electronics, and optics. Cr2O3 is well suited for wear resistance applications, as it is one of the hardest oxides with 29.5 GPa hardness. Several deposition techniques have been tried for making these coatings. Cr2O3 coating hardness can vary substantially due to compositional and microstructural variations, depending on the deposition method. Hardness of a plasma-sprayed Cr2O3 coating, 50 lm thick was about 14.7 GPa, while a 200 nm thick RF-sputtered chromium oxide coating, stoichiometrically close to Cr2O3, exhibited 30 GPa hardness combined with good scratch resistance. Even for the bulk Cr2O3, hardness values reported were from 9 GPa to 29.5 GPa. Hones et al. investigated a correlation between the hardness and the sputtering deposition parameters, i.e. oxygen partial pressure and substrate temperature, and found favorable deposition conditions with an oxygen partial pressure of about 15–20 % of the total sputtering gas pressure at substrate temperatures exceeding 500 K. Good coating adhesion is required for wear and corrosion resistance applications. Premature failure can occur for many reasons including coating delamination, cracking and plastic deformation. In addition to this, thin ceramic PVD coatings usually have columnar grain structure with micro cracks, pinholes, transient grain boundaries and often high throughcoating porosity, which all lead to accelerated pitting corrosion and failure at the coating/substrate interface, especially in hostile environments. On the other hand, several studies showed that coating thickness plays an important role in enhancing both PVD-coated tool cutting performance and resistance to abrasive and erosive wear. Graded systems have been employed to obtain thicker coatings without losing performance in terms of coating adhesion and toughness. It is likely that thicker coatings will improve corrosion resistance in aqueous environments by eliminating through-thickness pin-hole defects. Coating mechanical, adhesion and wear properties are strongly affected by microstructure. Interfaces with high adhesion are known to ensure prolonged coating life and good wear resistance. Sputtered coating microstructure and physical characteristics depend on the deposition parameters. Also, substrate surface conditions prior to deposition, characterized by surface roughness, stress and oxidation state, play an important role in controlling coating properties. In this paper SEM and TEM techniques were used to characterize thicker chromium oxide coating interfacial microstructure as a step towards developing a unique method for depositing thicker coatings with small grains, smooth surface and low residual stress.

Electroless deposition process has undergone numerous changes to meet the challenging needs for a variety of industrial applications ever since the invention of the process during 1947. Among the various metals that can be electrolessly plated, electroless nickel has proved its supremacy for producing coatings with high corrosion resistance, hardness, wear resistance and uniformity. Electroless nickel can be deposited from a variety of baths and the coating properties depends upon the type of reducing agents and other deposition conditions. Electroless nickel–boron coatings have received considerable interest nowadays because of the superior hardness, corrosion and wear resistance characteristics. In this paper, the authors have reported on the development of a biodegradable electroless Ni–B bath and evaluated its characteristic properties. The influence of bath constituents, temperature and pH on the rate of deposition was studied. Scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectroscopy and atomic absorption spectroscopy techniques were employed to find out the deposit morphology and boron content in the deposits. The hardness and wear resistance of the deposits were evaluated in the as deposited and heat treated conditions. The influence of sodium hypophosphite as reducing agent on the Ni–B deposit has also been studied. The use of nickel methane sulphonate as the metal ion source increases the bath lifetime without adversely affecting the deposit qualities. Annealing the Ni–B deposit at 400°C for one hour resulted in an increase in the hardness and thereby the wear resistance. The corrosion resistance of as plated electroless Ni–B deposit is higher than the heat treated deposits. Also, the corrosion resistance is highly enhanced by the incorporation of phosphorous to the nickel–boron alloy coating.

Sliding wear and solid-particle erosion resistance of a novel high-tungsten Stellite alloy

Double cemented (DC) carbide [1–3] is a novel dual composite composed of granules of conventional cemented carbide (WC + Co) dispersed in a metal matrix, typically cobalt (see Fig. 1). This concept of a “composite-within-a-composite” facilitates microstructural design to optimize properties for different applications. Properties of the overall composite are variable through control of granule and matrix properties, granule size and volume fraction, typically 70 to 90%. Granule properties are controlled by the grade of cemented carbide granules, i.e., Co content and WC particle size. Matrix properties are controlled by the matrix metal employed, modifiable through alloying or heat treatment. Studies to date have shown that this microstructural flexibility can achieve unusual combinations of properties, such as improved toughness and wear resistance compared to conventional cemented carbide, due to the larger metal matrix mean free path [2]. The particulate nature of the granules enables fairly conventional powder processing. DC carbide is currently being introduced in oil well drill bit inserts and should have use in many other applications requiring combined wear resistance and toughness. This material is also an ideal model for systematically investigating the microstructure/property relationships of a particulate reinforced dual composite, a design concept readily extendable to other metal and ceramic systems. Prior studies by others have investigated particulate dual composites containing lower volume fractions of cemented carbide granules in steel matrices [3–7] to improve wear and thermal shock resistance. Several

Formation of hard tungsten boride layer by spark plasma sintering boriding

Several double anodic oxidation coatings were formed on aluminum under different anodizing conditions (such as bath temperature and current density) and the effiects of anodizing conditions on surface properties and structure of coatings were studied. A hard anodized coating of excellent surface properties was obtained under a constant current density of 4Amp/dm2, in which the 1st layer (upper layer) was formed by the ordinary anodizing method (20°C, 30min.) and the 2nd layer (lower layer) was formed by the hard anodizing method (-5°C, 30min.). In particular, the coating formed by the 1st anodizing at 10°C for 30min. and the 2nd anodizing at -5°C for 30min. showed few cracks, a very plain surface, and a high wear resistance. When the bath temperature was constant at -5°C, the coating formed under a low current density in the 1st anodizing and under a high current density in the 2nd anodizing showed a wear resistance higher than that formed by the reverse order of treaments. However, the double anodic oxidation coatings under differrent current densities showed little differences in wear resistances according to the order of treatments for the 1st and 2nd processes; in contrary to the same conditions (with respect to the order of treatments) in different bath temperatures. The effect of structure of the cell on wear resistance was pursued. The coating formed under the condition for a large cell size in the 1st layer and a small cell size in the 2nd layer showed a remarkable decrease of wear resistance near the interface of the two layers. On the contrary, a high wear resistance was obtained by the reverse condition; that is, the condition for a small cell size in the 1st layer and a large cell size in the 2nd layer.

A kind of TiB2/Mo2FeB2 composite powders for reactive thermal spraying (RTS) and atmospheric plasma spraying (APS) were prepared using Mo powder, Fe-B alloy powder, Fe powder and TiB2 powder. The TiB2/Mo2FeB2 composite ceramic coatings were synthesized and deposited by APS and RTS on Q235 steel. Microstructure and phases were investigated by X-ray diffraction (XRD) and scanning electrical microscopy (SEM). The thermal shock resistance, wear resistance and corrosion resistance were characterized with the relevant lab testing equipment. The result indicates that the coatings are composed of the major phases Mo2FeB2, TiB2 and α-Fe, a little of Fe2O3, FeO, and B2O3.The thermal shock times of RTS-sprayed coatings is 44, the corrosion resistance is 6.07 times than those of the substrate, respectively, while those of APS-sprayed coatings are 55 and 15.5, respectively. The mass loss of Q235 steel is 138.6g/m2, while the mass loss of the coatings with 30% TiB2 which were prepared by RTS is 28.0952g/m2, the mass loss of the coatings with 30% which were prepared by APS is 15.4028g/m2, when the testing load was 400N. Therefore, the coatings with 30%TiB2 prepared by APS possess better wear resistance than the Q235 steel substrate.

ABSTRACTIt is a safe and low-cost new heat storage method to realize sensible heat storage at medium and high temperature by using flowing inorganic inert solid particle materials. The cost and performance of granular heat storage medium are very important for this kind of heat storage technology. The yellow sand in southeast of Tenggri Desert in Ningxia is studied. By thermal shock and grinding methods, the tests of thermal shock-resistance and wear resistance were carried out, under laboratory conditions, for the unscreened raw sand and the screened sand samples with three grain sizes (40–60 mesh, 60–80 mesh, and 80–100 mesh). The particle size of the raw sand is 150–300 µm (60–100 meshes) accounts for 60% (wt %) or more and meets the requirement of heat storage material. The density, thermal conductivity, and specific heat of raw sand are higher than those of three kinds of screened sand. Thermal shock and grinding affect the particle size distribution, density, specific heat, and thermal conductivity of the particles. The degree of influence varies with the particle size. The volume ratio heat capacity is used to measure the heat storage performance of the particles. Thermal shock results in a better thermal storage performance of the screened sand than the original sand. After comprehensive analysis of the properties of three kinds of screened sand, it is found that the content of 60–80 mesh-screened sand (31.75%) is the highest in the original sand. After thermal shock and grinding, the screened sand not only has good heat storage performance (average volumetric specific heat capacity 3.232 J· K−3· K−1), but also has the smallest change of particle size (breaking rate is less than 24, and agglomeration rate is less than 6), and the thermal shock resistance and wear resistance are outstanding. It is suggested that the screened sand with the particle size range of 200-300µm (60–80 mesh), also the particles with the highest content in the original sand, should be selected as the solid particle flowing heat storage medium.

Ceramic-metal composites, or cermets, are used for a variety of applications. In general, the ceramic phase provides hardness or wear resistance while a continuous metal phase acts as a binder and provides toughness. The alumina-based cermets described here are unique in that the metallic phase (platinum) is discontinuous and constitutes only about 1 to 2 vol % of the structure. This material was developed to serve as a high-temperature electrical insulator under conditions of severe thermal shock. Because of the small grain sizes involved, electron microscopy was used to study the relation between properties and process variables as well as to better understand the mechanism of thermal shock resistance.Platinum was intimately mixed with alumina powder by precipitation from a PtCl4 solution followed by drying. The resulting powder mixture was hot-pressed in a graphite die at 1610°C for 15 min under 69 MPa (10,000 psi) pressure. Cermets produced from Alcoa A-17 alumina powder had a final grain size of 15 ± 4 μm, while Fisher Scientific reagent-grade alumina resulted in a grain size of 4 ± 1 μm. The platinum particles ranged from 0.2 to 1.0 μm in diameter. Thermal shock resistance was tested by heating the cermet to 520°C and quenching in hot water. Cermets that were gastight after 15 quench cycles were considered acceptable. Thermal shock resistance was improved by heating the as-pressed pellet to 1630°C and air cooling.

Balance between strength and ductility of dilute Fe2B by high-throughput first-principles calculations

The demand for advanced coating materials in high-temperature and wear-resistant applications has led to the exploration of multicomponent systems that offer superior mechanical properties. Among these, AlCrSiN has emerged as a promising candidate owing to its ability to blend the thermal stability and hardness of AlCrN aided by grain refinement along with the presence of amorphous phase as a result of silicon addition. In this study, SS 304 substrates were used to deposit AlCrSiN thin films through magnetron sputtering process. This work focuses on the structural, hardness, scratch, wear and adhesion properties of AlCrSiN thin films as a function of substrate temperature. The AlCrSiN coating deposited at 400°C exhibited a hardness of 23 GPa and an (H/E) ratio of 0.08, which is an apparent measure of good wear-resistance coating. The work of adhesion significantly increased from 18 to 150 Jm −2 as the substrate temperature was gradually boosted from 30 to 500°C. Coatings facricated at room temperature and 300°C displayed an amorphous structure, while those deposited at 400°C and 500°C developed CrN/AlN crystallites averaging 16 nm in size within the amorphous matrix. Furthermore, the coefficient of friction (COF) was maintained between 0.27 and 0.30. These findings underscore the potential of AlCrSiN coatings to enhance the wear resistance and mechanical performance of substrates in demanding industrial applications, with substrate temperature playing a key role in optimizing coating properties.

Effect of sediment concentration and particle size on erosion behavior of forged stainless steel

The present article describes in detail the wear behavior of rutile-reinforced LM13 alloy composite at elevated temperatures. Rutile particles in different amounts were reinforced into LM13 alloy by the stir casting route. The microhardness measured at different areas indicates good interfacial bonding. Wear tests were conducted for composites containing rutile particles in 10 wt.% and 15 wt.% with variation in particle size (50–75 µm and 106–125 µm). The presence of ceramic particle in the matrix improves the hardness, wear resistance, thermal stability, and durability of the materials. The wear of composite at 200°C presented entirely different wear behavior mode than that at 250°C. The wear rate of fine size reinforced composite was substantially lower than that of coarse size reinforced composite with higher load at 200°C. A transition from mild-to-severe wear in composite was observed with higher load above 150°C. The morphology of wear track and debris indicates that nucleation of cracks around the void on the interface of the particles is the main cause of surface damage.

The present study investigates the mechanical performance of gel-cast fused silica composites doped with bio-waste-derived natural silica. Natural silica was extracted from rice husk, and ceramic composites were fabricated using gel casting. The tribological performance of the composites was evaluated in terms of wear rate and coefficient of friction, and mechanical performance was assessed in terms of hardness and compressive strength. Results revealed that silica doping at 10wt% significantly enhanced wear resistance and increased the hardness from 486 HV to 569 HV and compressive strength from 0.79 GPa to 2.17 GPa. However, at 15wt% doping, wear resistance deteriorated due to structural inconsistencies, reducing hardness to 535 HV and compressive strength to 1.43 GPa. Further insights were gained through Fourier transform Infrared spectroscopy (FTIR) analysis, which confirmed silica presence with characteristic absorption peaks at 805cm-1 and 1100cm-1. Additionally, ANOVA and regression analysis established that material composition and applied load were the most influential factors, accounting for 97.57% of wear rate variation. This study provides a foundational benchmark for optimizing silica-doped ceramics in wear-resistant applications.

As advancements in lightweight and synthetic materials have evolved, our ability to tailor materials to meet societal demands has expanded. Aluminium alloys, known for their high strength-to-weight ratio and cost-effectiveness, are extensively utilized in engineering applications, including structural casting and automotive components. This study employed the stir casting method to investigate the impact of silicon carbide (SiC) and graphite (Gr) on a hybrid A356 composite, aiming to enhance its tribological applicability. SiC and Gr particles were processed using a vibratory ball milling machine for two hours, followed by composite fabrication with varying particle sizes. Microstructural investigation using optical microscopy revealed maximum hardness values of 127 BHN and 125 BHN for A356 composites reinforced with 12.50% SiC, 15.50% Gr, and 11.43% SiC, 15.86% Gr, respectively. Wear rate analysis demonstrated that reinforced A356 composites exhibited higher wear resistance compared to unreinforced alloys. Notably, the sample reinforced with 11.43% SiC and 15.86% Gr displayed exceptional wear resistance. Photo micrographs of A356-SiC-Gr samples at different sliding distances, velocities, and loads revealed minimal plastic deformation during wear testing, resulting in abrasive and cohesive wear. Overall, this study underscores the effectiveness of graphite (Gr) and silicon carbide (SiC) as reinforcement materials for enhancing the tribological properties of A356 composites.