Effect of Additional Particulate Reinforcement on the Properties of Fibrous Ceramic Matrix Composites

Composites, generally, consist of two phase i.e. matrix and reinforcement. Here in this work additional phase in terms of micro/nano particles was added in the fiber reinforced ceramic matrix composites and its effect on the final properties of composites was studied. Composites were prepared using sol derived from Tetraethoxysilane (TEOS) and Dimethyldiethoxysilane (DEDMS), and polycarbosilane (PCS) as matrix precursors and SiC fabric as reinforcement. To some composites another phase of solid, micro/nano powder precursor of SiC was added to decrease number of impregnation cycles. Latter composites resulted in higher density. Green composites were post-cured and pyrolyzed. Some of the composites were heated to 1500 °C in argon atmosphere. Composites were characterized for density, microstructure and mechanical properties. It revealed that the resulting matrix was solid glass and addition of SiC powder facilitated the rapid densification. Composites prepared with SiC nanoparticles as well as SiC fabric as reinforcement exhibit higher flexural strength than those made without nanoparticles. The fracture behaviour is also seen to be of mixed mode failure type

Effect of applied pulse voltage on nitrogen plasma immersion ion implantation of AISI 316 austenitic stainless steel

Plasma immersion ion implantation (PIII) of nitrogen was performed for 4 h on AISI 316 austenitic stainless steel substrates at a temperature of 400 °C. The substrate bias was varied between -1 and -20 kV with different duty cycles so as to keep the substrate temperature fixed. The implanted ions were evident to the depths of a few microns, which is much greater than their implantation depths, resulting in an enhancement of surface microhardness. A load dependent surface microhardness is observed which is nearly independent of the applied bias. Glancing angle X-ray diffraction patterns indicate the formation of expanded austenite at all biases. X-ray photoelectron spectroscopy indicates the formation of CrN in the first 175 Å of the surface for high bias. The results indicate that if implantation accompanies diffusion, then PIII at low bias is suitable enough for nitrogen incorporation in materials. Lower voltages also mean greater conformity between the ion sheath and the sample surface, and hence better treatment uniformity

Plasma polymerization using a constricted anode plasma source

This paper investigates plasma polymerization of hexamethyl disiloxane (HMDSO) using a constricted anode plasma source (CAPS). The CAPS uses a new electrode configuration i.e. a small anode surrounded by a large cathode, which allows a plasma to be sustained at low pressure of 1× 10-3 mbar. Using CAPS, polymerization of HMDSO in the presence of oxygen was carried out, which resulted in the formation of pinhole free glass-like coating on aluminum substrates. The coating was analysed using X-ray photoelectron spectroscopy, which confirmed the presence of the Si-O-C and the SiOx. Near the coating surface more oxygen was obtained than in the bulk of the coating. With the increase in the deposition temperature, the carbon content in the coating decreased. The corrosion resistance also increased with the increase in deposition temperature. The results establish that the new electrode configuration used in the present investigation can produce good quality coatings by polymerization of a precursor

Low energy isothermal plasma-immersion ion implantation of nitrogen for enhanced hardness of AISI 52100 ball bearing steel

Plasma immersion ion implantation (PIII) is an advanced, plasma-assisted surface engineering technique to enhance resistance to wear, corrosion, etc. The present study concerns PIII of nitrogen ions in AISI 52100 ball bearing steel at low energy (~1 keV) to increase the hardness. The substrate temperature was independently varied up to 500°C with a heater to facilitate diffusion of the implanted ions during PIII. Microhardness measurements reveal a significant increase in hardness within the implanted zone or case extending up to approximately 40 µm following PIII carried out isothermally at a temperature between 300 and 500°C for 3-5 h. X-ray diffraction analysis indicates that PIII results in the formation of three varieties of iron-nitrides, which have also been detected by X-ray photoelectron spectroscopy (XPS). However, these nitrides are too fine to be resolved under the optical microscope. Auger electron spectroscopy (AES) shows that the nitrogen penetration depth is greater than the case depth, determined separately by a cross-sectional microstructural study and hardness measurements. Finally, a simple kinetic analysis reveals that nitrogen diffusivity in the present PIII study is an order of magnitude faster than the relevant diffusion rate of nitrogen in steel

A study of martensitic stainless steel AISI 420 modified using plasma nitriding

We studied martensitic stainless steel AISI 420, modified using glow discharge plasma nitriding. Microhardness measurements, X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to investigate the surface microhardness, crystal structure, microstructure and chemical bonding in the modified surfaces. High surface microhardness (~1300 HV) over a case depth of about 60 microns is obtained. Glancing incidence X-ray diffraction (GIXRD) indicates the presence of a predominantly Fe3N phase with dispersed CrN within 2-5 microns on the surface. In addition, using Bragg-Brentano geometry, we measured the presence of a minor phase of Fe4N in the case depth. SEM confirms that the microstructure within 2-5 microns of the surface is different from that of the bulk. XPS shows nitride phase formation on the surface. AES measured over the cross-section of the case depth shows a direct relation of the increased surface microhardness to the high nitrogen content

Characterization of surface microstructure and properties of low-energy high-dose plasma immersion ion-implanted 304L austenitic stainless steel

Low-energy plasma immersion ion implantation (PIII) of nitrogen was carried out in pulses of 3.8-kHz frequency to modify the surface of AISI 304L stainless steel at a high dose of 0.7-2.1×1023 ions/m2 at -1 kV applied d.c. potential in the temperature range 300-380 °C. PIII seems to significantly enhance the hardness up to a shallow depth from the surface but adversely affect the resistance to pitting corrosion. A detailed characterization of the surface microstructure, composition and chemical state of the constituents was carried out by normal incidence and glancing angle X-ray diffraction (XRD) and by X-ray photoelectron spectroscopy (XPS), respectively. XRD analysis revealed that the microstructural constituents were mostly austenite (γ), expanded austenite (γN) and var epsilon-nitride in varying proportion depending on the PIII parameters. On the other hand, XPS analysis showed that nitrogen was mostly present as Fe- or Cr-nitride. In particular, γN phase seemed to be a mixed nitride of Fe and Cr. While significant increase in hardness could arise due to grain refinement of γ and γN (<50 nm) and solid solution hardening due to nitrogen, the deterioration of corrosion resistance could be attributed to the evolution of a multiphase microstructure (γ, γN and particularly εN) from an essentially single-phase parent γ microstructure. Finally, a detailed analysis is presented to identify the optimum PIII condition that offers a compromise between increase in hardness and loss of pitting corrosion resistance

Influence of alloying elements on the corrosion properties of steels during plasma nitriding process

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450°C. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This is due to the presence of iron nitrides and few chromium nitride phases. In this study an attempt is made to study the effect of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels during plasma nitriding. The effects of plasma nitriding on corrosion were investigated by performing potentiodynamic tests on untreated and treated steels. The phases responsible for the improvement in corrosion resistance were detected by X-ray diffractometer. It was found that low alloy steels performed better compared to the other steels because of the presence of Fe4N, Fe3N and other nitrides, which form a dense protective layer responsible for corrosion resistance

Studies on low-energy nitrogen plasma immersion ion implantation on austenitic stainless steel and Cu-strengthened HSLA-100 steel

Low-energy (~1 keV) nitrogen plasma immersion ion implantation was used to modify austenitic stainless steel and Cu-strengthened HSLA-100 steel. The variable implantation parameters were treatment time, gas composition and treatment temperature. For austenitic stainless steels, it was found that the expanded austenite phase formed by low-temperature implantation, did not always prove to be corrosion resistant, though there was an increase in the hardness. For Cu-strengthened HSLA-100 steel, an enhancement in the linear strain to failure under embrittling conditions was observed, which was due to introduction of residual compressive stresses as well as reduction in the hydrogen flux. The results emphasize the use of low energy in Plasma Immersion Ion Implantation (PIII) and its applicability to solving different surface engineering problems

Electronic structure, microstructure, and crystal structure of the precipitation-hardened alloy Cu<SUB>98</SUB>Be<SUB>1.8</SUB>Co<SUB>0.2</SUB>

Precipitation hardening of copper alloys results in improved elastic properties but is accompanied by reduction in electrical conductivity. We study the electronic structure, microstructure, and crystal structure of precipitation-hardened Cu:Be:Co (98:1.8:0.2 weight %) alloy to look for coupled changes accompanying the precipitation hardening. X-ray diffraction is used to study the strain in the Cu matrix upon Guinier-Preston zone formation and the subsequent precipitation. Using x-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM), we compare the Cu matrix and Co beryllides of well-characterized as-obtained and precipitation hardened alloys. SEM confirms the evolution of the microstructure typical of Guinier-Preston zone formation and precipitation. The binding energies and line shapes of Cu 2p, Co 2p, and Be 1s core levels are investigated using XPS. In spite of the Co beryllides migrating to the grain boundaries as an entity, XPS indicates that the Be atoms get oxidized upon migration, while the Co atoms remain metallic. The Cu 2p core levels shift 0.3 eV to higher binding energy in the as-obtained and partially hardened alloys. In addition, a line shape change observed only in the partially hardened alloy is attributed to strain in the Cu matrix upon Guinier-Preston zone formation. In contrast, for the fully hardened alloy, the binding energy and line shape reverts back to that of pure copper. But for the chemical potential shift, the valence band spectral features exhibit negligible changes in spectral shape upon hardening. The results are consistent with a change in the chemical potential due to metastable Co beryllides and increasing strain in the initial stages of hardening due to Guinier-Preston zones. In the fully hardened alloy, the observed reduction of the chemical potential shift is related to precipitation and a corresponding readjustment of the Fermi energy

Low- and high-energy plasma immersion ion implantation for modification of material surfaces

Low- and high-energy plasma immersion ion implantation (PIII) of nitrogen has been performed on austenitic stainless steel and high-carbon low-alloy steel to modify their surface properties. In the case of austenitic stainless steel, an expanded austenite layer with surface microhardness of 650 HV was formed with a thickness of 7-8 μ m for an elevated treatment temperature of 400 °C, irrespective of the treatment energy. X-Ray photoelectron spectroscopy (XPS) investigations revealed that, at high energy, nitrogen is in a bound state and chromium nitride is formed in the subsurface region, followed by expanded austenite. In the case of high-carbon low alloy steel, the diffusion coefficient of nitrogen obtained by PIII is higher than that obtained by glow-discharge plasma nitriding. The results indicate that if implantation is followed by diffusion, low-energy PIII gives similar or better results than high-energy PIII as far as the treated layer thickness, phase formation and microhardness are considered. Low-energy PIII has a lower hardware cost and reduced sheath dimensions, and thus uniformity in surface modification is achieved