Laser material processing of nickel superalloy for improved erosion resistance

A nickel-based superalloy was laser surface treated, and its erosion behavior was evaluated. The laser power and scan speed were varied in different levels to impart variations in microstructure and mechanical properties. The microstructure of specimens exhibited fine equiaxed grains to columnar structure at different parameters. A high cooling rate improved the hardness of the laser-treated specimen up to 603?HV_0.3 compared to the base material hardness of 430?HV_0.3. The rate of erosion increased linearly from 30° to 60° impingement angle and decreased at 75° impingement angle. The accumulation of the erodent inside the crater and the consequent absorbtion of the incident kinetic energy might have caused this reduction. The laser surface treated specimens exhibited ～1.5 factor of improvement in high temperature erosion resistance. This was attributed to the minimized energy transfer from impinging particle to the substrate achieved through laser surface melting.     

Solid-particle erosion behavior of high-performance thermoplastic polymers

Solid-particle erosion tests were carried out to study the effect of matrix material, impact angle, and impact velocity on the erosion behavior of seven types of thermoplastic neat polymers (i.e., polyetherimide, polyetheretherketone, polyetherketone, polyphenylene sulfide, polyethersulfone, polysulfone, and ultrahigh molecular weight polyethylene). Steady-state erosion rates of these polymers have been evaluated at different impact angles (15–90°) and impact velocities (25–66 m/s). Silica sand of particle size 200 ± 50 μm was used as the erodent. These polymers have exhibited maximum erosion rate (E _max) at 30° impact angle indicating ductile erosion behavior. Some of these polymers have shown an incubation behavior at lower impact velocities for an impact angle of 90°. Correlations among steady-state erosion rate and mechanical properties and glass transition temperature (T _g) were established. Morphology of eroded surfaces was examined using scanning electron microscopy and possible wear mechanisms were discussed.

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Photoluminescence investigations on alumina ceramic bearing couples tested under different angles of inclination in a Hip joint simulator

Aseptic loosening due to wear and dislocation of the implant represents the main complication after total hip arthroplasty. To gain more insight into the influence of the implant position on wear, commercial alumina couplings have been tested in a hip joint simulator under three different angles of cup inclination (23°, 45°, 63°) with respect to a horizontal plane. The planned length of the test was ten million cycles. However, the test was stopped at 5.5 million cycles due to the fracture of one of the femoral heads, tested with at angle of 63°. The residual stress state in the worn acetabular cups and in the fractured femoral head were evaluated by the frequency shift and broadening of the R₁ and R₂ fluorescence bands due to the Cr³⁺ ions naturally present in alumina ceramics as trace impurities. The gravimetric measurements did not show significant differences among the three different inclinations tested, in agreement with previous simulator studies, but in disagreement with in vivo findings. The fluorescence measurements allowed to affirm that an angle of 63° represents a worsened mechanical condition for the prosthetic component, with a consequently higher probability of fracture and/or damage potentially conducive to massive wear. In the light of the fluorescence results, it did not appear surprising that the femoral head that fractured was the one being tested at 63°.     

Investigation of erosive wear behavior and physical properties of SGF and/or calcite reinforced ABS/PA6 composites

The aim of this study was to investigate the erosive wear behavior of glass fiber, CaCO₃ particle and glass fiber/CaCO₃ hybrid reinforced ABS/PA6 blend based composites. The samples were prepared by using melt mixing and injection molding techniques. The mechanical, thermal, morphological properties and erosive wear behavior were investigated in terms of reinforcing agent type and composition. It was observed that the tensile strength and modulus values of hybrid composites gave a value between tensile strength and modulus values of only fiber reinforced composites and only particle reinforced composites. From DSC analysis it was revealed that T_g and T_m of composites were not significantly affected by reinforcement; however, degree of crystallinity was found to be sensitive to reinforcement type and composition. The impingement angle was found to have a significant effect on the erosive wear behavior. The results indicated that composite materials exhibited maximum erosion rate at impact angle of 30° conforming their ductile erosion behavior. In order to investigate wear mechanisms, eroded surface analysis was done by scanning electron microscopy. Surface analysis showed that repeated impact of hard silica sand particles caused a local removal of the matrix from the fiber surface and led to form craters on the surface of the composite material.     

Surface integrity studies on abrasive water jet cutting of AISI D2 steel

This article investigates the 3D surface topography and 2D roughness profiles, and micrographs were analyzed in the abrasive water jet (AWJ) cutting of AISI D2 steel kerf wall cut surfaces by varying water jet pressures and jet impact angles. In 3D surface topography, roughness parameters such as Sq, Ssk, Sp, Sv, Sku, Sz, and Sa were improved by various jet impact angles with different water jet pressures. However, the roughness parameters Ssk and Sku strongly depend on the water jet pressure and jet impact angle. This is confirmed by kerf wall cut profile structures. Fine irregularities of peaks and valleys are found on the AWJ cut surfaces, as evident from 2D roughness profiles. The scanning electron microscope micrographs confirm the production of an upper zone not very much damaged and a lower striation free bottom zone, by using the jet impact angle of 70° with a water jet pressure of 200?MPa. Finally, the results indicate a jet impact angle of 70° maintaining the surface integrity of D2 steel better than normal jet impact angle of 90°. The results are useful in mating applications subjected to wear and friction. This has resulted in enhancement of the functionality of the AWJ machined D2 steel components.     

Influence of yttrium dopant on the synthesis of ultrafine AlN powders by CRN route from a sol–gel low temperature combustion precursor

Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al₂O₃, C and Y₂O₃ prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO₃, Al₃Y₅O₁₂ and Al₂Y₄O₉, which formed a liquid at about 1400 °C and promoted the transformation of Al₂O₃ to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150 °C, and Al₂O₃ transformed to AlN completely at 1450 °C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450 °C were 150–300 nm.     

Hydroxyapatite/SiO2 Composites via Freeze Casting for Bone Tissue Engineering

Freeze casting is a fabrication method that allows producing near‐net‐shaped ceramics with variable porosity. Hydroxyapatite (HA) was modified by the addition of different amounts of SiO₂ nanoparticles during freeze cast preparation. The addition of SiO₂ introduced a partial phase transformation of HA to β‐tricalcium phosphate and improved the form stability due to less shrinkage after sintering. The impact of surface roughness of pure HA ceramics and the influence of SiO₂ introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast‐like cells (MG‐63) was investigated. While both cell attachment and proliferation of smooth pressed HA was significantly enhanced compared to rough freeze cast HA, the addition of SiO₂ improved the cell numbers of the latter. The expression of cell differentiation markers osteocalcin and collagen I was found to be supported by rough surfaces (R_a = 5–6 µm) in particular on ceramics containing SiO₂     

Sliding wear and solid particle erosion response of aluminium reinforced with tungsten carbide nanoparticles and aluminide particles

In the present effort, aluminium matrix composites (AMCs) were produced by the addition of submicron‐sized WC particles of low (up to 2.5 vol%) content into a melt of Al1050. Casting was assisted by the use of K₂TiF₆ as a wetting agent and mechanical stirring in order to limit particle clustering. Particle distribution was reasonably uniform comprising both clusters and isolated particles. Various different reinforcing particles' phases were identified, both in situ (Al‐W, Al‐Ti, and Al‐W‐Ti intermetallic phases) and ex situ (WC particles) of various morphologies shapes and sizes. Increase of the reinforcing particle content led to an increase of the tendency for clustering. The wear properties of the composite were examined by dry sliding wear. The worn surfaces and the produced debris were examined by SEM‐EDX, and an effort to correlate the wear response of the produced materials with the matrix and the reinforcing phase characteristics was attempted. In general, the increase of the reinforcing phase content led to an improvement of the sliding wear response. Solid particle erosion experiments were carried out for impact angles of 30°, 60°, and 90°. Τhe eroded surfaces were examined with SEM‐EDX, and possible erosion mechanisms were proposed based on morphological and other material characteristics. Intensive particle clustering seemed to deteriorate the erosion resistance of the systems. Medium concentrations of the reinforcing particles (1.0‐1.5 vol% WC) are proposed as a recipe for optimum sliding wear and solid particle erosion resistance behavior.     

Impact of high‐velocity oxy‐fuel sprayed TiAlN surface coating on mechanical and slurry erosion performance of aluminium alloys

TiAlN coatings were deposited on AA1050 and AA5083 aluminium alloys by high‐velocity oxy‐fuel (HVOF) spray process and evaluated for their mechanical and slurry erosion performance. In comparison to base alloys, the mechanical properties were found to enhance upon coating. The effect of working parameters namely impingement angle, impact velocity, erodent size and erodent feed rate on the slurry erosion wear rate has been investigated. The slurry erosion wear rate of the uncoated samples was found to decrease with an increase in the impingement angle whereas for coated samples the slurry erosion wear rate first increased, reached to a maximum value at 60° and then decreased with further increase in the impingement angle. For uncoated and coated samples the slurry erosion wear rate was found to increase with an increase in impact velocity, erodent size and erodent feed rate. Finally, the morphology of the eroded surfaces was analyzed using scanning electron microscopy and the possible erosion mechanisms have been studied.     

Effects of substrate material on diamond growth from CO-H2 plasma

Diamond synthesis from CO-H₂ plasma has been carried out on various substrate materials, e.g. metals: nickel, cobalt, tungsten, molybdenum, copper and ceramics: SiC, SiO₂, Al₂O₃, ZrO₂, AlN. Diamond formation was confirmed on every substrate with the exception of cobalt and nickel. The highest density of diamond nucleation, over 10⁸ cm^–2, was obtained on amorphous SiO₂, the carbide-forming metals tungsten and molybdenum and on SiC; on these the nucleation density was one order of magnitude higher than on the other substrates. Diamond films prepared on tungsten, molybdenum and SiC substrates had a strong adhesion force: 1.3 to 1.5 kg mm^–2.     

Preparation and properties of mullite-bonded porous SiC ceramics using porous alumina as oxide

Mullite-bonded porous silicon carbide ceramics were prepared by an in situ reaction bonding technique and sintering in air with SiC, porous Al₂O₃, and graphite as starting materials. The pores in the ceramics were formed by burning graphite and by stacking particles of SiC and Al₂O₃. The surface of SiC was oxidized to SiO₂ at high temperature. With a further increase in temperature, SiO₂ reacted with Al₂O₃ to form mullite. The reaction-bonding characteristics, phase composition, open porosity, mechanical strength as well as the microstructure of porous SiC ceramics were investigated.     

Process and wear behavior of monolithic SiC and short carbon fiber-SiC matrix composite

The process and wear behavior of monolithic SiC and 10 vol. % short carbon fiber-SiC matrix (C-SiC) composite have been studied. The results indicate that, among ethyl alcohol, acetone, n-hexane and n-octyl alcohol, n-octyl alcohol was the most effective dispersing agent in dispersing both SiC powder and short carbon fiber. Among AlN, Al₂O₃, B₄C, graphite, AlN/B₄C, AlN/graphite, B₄C/graphite and Al₂O₃/B₄C, the most effective sintering aid for the fabrication of SiC and C-SiC composite was a mixture of 2 wt% AlN and 0.5 wt% graphite. The monolithic SiC hot-pressed at 2100°C exhibited higher density but lower flexural strength than those hot-pressed at 2000°C due to a grain growth effect. For the C-SiC composite, both density and strength of the composite hot-pressed at 2100°C were generally higher than those hot-pressed at 2000°C. The density and strength of C-SiC composite were lower than those of monolithic SiC under the same hot pressing conditions due to a higher porosity level in the composite. When monolithic SiC slid against C-SiC composite, the weight losses of SiC and the composite were each less than that of self-mated SiC or self-mated C-SiC. In the self-mated SiC tribosystem, a mechanically stable film could not be established, resulting in an essentially constant wear rate. When sliding against C-SiC, a thin, smooth and adherent debris film was quickly formed on the SiC surface, resulting in a lower wear.     

Influence of annealing duration on the erosive wear behavior of polyphenylenesulphide composites

The influence of annealing duration on the erosive wear behavior of short glass fiber (40% w/w) and CaCO₃ mineral particulate (25% w/w)–short glass fiber (40% w/w) (total: 65% w/w) reinforced PPS composites has been characterized under various experimental conditions by differential scanning calorimetry (DSC) and erosion measurements. The erosive wear of the composites have been evaluated at different impingement angles (30, 45, 60, and 90°) and at four different annealing periods (30, 60, 90, and 120 min). Increase in the total crystallization causes an improvement in the erosive wear properties of the samples. Annealing time controls the morphology by influencing the degree of crystallinity in the matrix and in the fiber–matrix interface. This formation restricts fiber–matrix debonding. There is no linear proportionality between annealing time and relative degree of crystallization. The results indicate that PPS composites show maximum in wear versus impact angle relation at 60° confirming their semi-ductile failure behavior. The morphologies of eroded surface are examined by the scanning electron microscope.     

A study on the abrasive and erosive wear behavior of arc-deposited Cr-N-O coatings on tool steel

In this study, the cathodic arc evaporation technique, by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases, was utilized to deposit three different Cr-N-O coatings (CrN, CrN/Cr(N,O), CrN/Cr₂O₃) on AISI M2 tool steel. Two types of wear tests were applied to evaluate the abrasive and erosive wear behavior of the coated and uncoated specimens. One was the ball-on-disk abrasion test to measure the friction coefficient of these specimens. The other was the erosion test using Al₂O₃ particles (~ 177 µm in size and Mohr 7 scale) of about 5 g, and then the surface morphologies of the eroded specimens were observed. To further understand the coating effects on the two wear behaviors of M2 steel, coating structure, morphology, and adhesion were analyzed using XRD, SEM, and TEM, respectively. The results showed that surface roughness and adhesion of the double-layered coatings (CrN/Cr(N,O) and CrN/Cr₂O₃) were inferior to those of monolithic CrN, but their hardness and elastic modulus were superior to those of CrN. In the abrasive behavior, Cr-N-O coatings reduced the friction coefficient of M2 substrate. In particular, the CrN/Cr₂O₃ has the highest hardness/elastic (H/E) modulus ration, therefore the lowest friction coefficient, among all the coated-specimens tested. In the erosive behavior, the coated specimens exhibited better erosion resistance as compared to the uncoated ones, at the impingement angles of either 30^o or 90^o. Moreover, the erosion resistance of CrN/Cr(N,O) coatings was superior to that of CrN/Cr₂O₃ coatings due to its better adhesion.     

ZrO_2－Al_2O_3－SiC系复相陶瓷材料的冲蚀磨损

本文对ＺｒＯ２增韧１０％ＳｉＣ／Ａｌ２Ｏ３基复合材料和ＳｉＣ颗粒弥散强化５％Ａｌ２Ｏ３／ＺｒＯ２基复合材料的冲蚀磨损的研究，实验表明：相交增初有助于断裂韧性的改善，从而缓和了材料的高角冲蚀率；高弹模量的ＳｉＣ二相粒子引入后基体材料的硬度增加，提高了材料的抗低角磨损能力．显微结构（ＳＥＭ）分析表明，不同的冲蚀角度条件下材料表面的损伤行为和磨损微观机制也不相同，通过ＰＵＤ计算，定量表征材料的抗切向磨损能力．     

Low-temperature sintering of SiC reticulated porous ceramics with MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> additives as sintering aids

SiC reticulated porous ceramics (SiC RPCs) was fabricated with polymer replicas method by using MgO–Al₂O₃–SiO₂ additives as sintering aids at 1,000∼1,450 °C. The MgO–Al₂O₃–SiO₂ additives were from alumina, kaolin and Talc powders. By employing various experimental techniques, zeta potential, viscosity and rheological measurements, the dispersion of mixed powders (SiC, Al₂O₃, talc and kaolin) in aqueous media using silica sol as a binder was studied. The pH value of the optimum dispersion was found to be around pH 10 for the mixtures. The optimum condition of the slurry suitable for impregnating the polymeric sponge was obtained. At the same time, the influence of the sintering temperature and holding time on the properties of SiC RPCs was investigated. According to the properties of SiC RPCs, the optimal sintering temperature was chosen at 1,300 °C, which was lower than that with Al₂O₃–SiO₂ additives as sintering aids.     

Erosion resistance of Co-Cr-Al coatings containing active element additions

Materials resistant to high temperature corrosion and small particle impact erosion are necessary in the design and construction of energy conversion systems. Al₂O₃-forming M-Cr-Al coatings with active element additions on an IN 738 substrate have exhibited enhanced resistance to erosion damage of their oxide scales owing to improved adherence of the scale. This improvement results from modifications of the scale morphology by the active element additions which encourage pegs of oxide that penetrate into the coating. Other active element additions cause a porous scale to form, increasing the erosion susceptibility. The thin alumina scales behave as a brittle material with the highest erosion rate occurring at an impingement angle of 90° and scale removal occurring by a chipping action.     

Magnetron sputter deposition of (SiC)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(AlN)<Subscript>x</Subscript> solid solution films

Magnetron sputtering of polycrystalline SiC-AlN targets was used to obtain films of (SiC)_{1− x} (AlN)_x solid solutions on silicon carbide (6H-SiC) substrates heated to a temperature in the range T = 500–1200°C. The deposits were characterized with respect to structure, composition, and optical absorption. It is demonstrated that the films obtained on 6H-SiC substrates at T ≥ 1000°C possess a single crystal structure. The compositions of (SiC)_1−x (AlN)_x films are close to those of the corresponding SiC-AlN targets.     

Interaction between silicon carbide and a nickel-based superalloy at elevated temperatures

A study has been made of the reaction of hot-pressed SiC and a nickel-based superalloy at temperatures between 700 and 1150° C. Under conditions of reduced oxygen pressure at the reaction interface, obtained by applying pressure to the couple, some degree of reaction was observed in both metal and ceramic at all temperatures studied. Preliminary studies utilizing the same techniques at 1000° C with a Si-SiC ceramic composite, Si₃N₄, MgO, Al₂O₃, and SiO₂ also indicated some degree of reaction in the metal for all ceramics examined.