Advanced Materials Research Vols. 83-86

Abstract: Three 0.15% carbon steel samples containing small additions of vanadium and nitrogen singly or in combination have been carburized in a natural Titas gas atmosphere at a temperature of 9500C and a pressure of about 15 psia for time periods ranging from 1 to 5 hours and quenched in 10% brine from the carburizing temperature of 9500C after pre-cooling to 8600C in the furnace followed by tempering at a low temperature of 1600C. The structure and properties of the carburized and heat treated specimens were studied systematically by optical microscopy, surface hardness and microhardness measurements, X-ray diffractometry and impact tests. It was found that vanadium without nitrogen does not have any effect in the formation of retained austenite while vanadium with nitrogen is effective in promoting the formation of retained austenite in the case of carburized and hardened steels. It was also found that vanadium alone and vanadium with nitrogen refine the martensite platelets (needles) in the case of carburized and hardened steels, vanadium with nitrogen being more effective. Microhardness measurements have shown that vanadium improves the case hardness and the core hardness values; vanadium with nitrogen is more effective than vanadium alone in increasing the case hardness and the core hardness. The hardenability is found to increase with the increase of austenite grain size and with the extent of carbon penetration of the case of carburized steels. Vanadium as vanadium carbide, VC are detrimental to toughness and vanadium as vanadium carbonitride, V(C, N) are beneficial to toughness of the core of low carbon steels in carburized and hardened condition.

Abstract: Traditional materials processing in the nanometer range using laser technology is very difficult with conventional optics due to the diffraction limit of the beam wavelength, a near-field technology has been developed to circumvent the diffraction limit, permitting the spot size to be reduced down to 20 nm. In most near-field techniques, this technology is achieved by placing a small aperture or microparticle between the sample and the light source. Therefore this paper will analytically investigate the profile of the intensity for diffraction of laser irradiating an aperture or microparticle in nanostructure processing. Classical electromagnetic wave theory is employed to calculate the intensity for diffraction of laser irradiating a microparticle or aperture. The results will reveal the differences between an aperture and micoparticle for diffraction of laser. The effect of laser parameters on the intensity and distribution of diffraction will be also discussed.

Abstract: The effects of load and temperature on wear behavior of 6061 Aluminum alloy matrix composite reinforced with 20% Al2O3 (submicron) particulates against AISI 4041 steel disc were studied at elevated temperatures ranging from 25oC to 300oC. Mild and severe wear regions separated by a transition region were observed at all temperatures with a difference of two orders of magnitude between mild and severe wear. The critical loads observed at 100oC, 200oC and 300oC were 40 N (2 MPa), 30 N (1.53 MPa) and 15 N (0.76 MPa) respectively indicating that wear resistance of the composite decreases with increase in temperature. Scanning electron microscopy revealed that wear was accompanied by extensive thermal softening of the matrix, in addition to particulate fracture due to high shear strain generated from the contacts and material transfer to the counterface. The wear rates were reduced in the mild wear regime due to oxidation of the iron counterface and deposition of oxides on the contact surfaces evident by EDS analysis.

Abstract: Metal matrix composites (MMCs) are engineering materials in which a hard ceramic component is dispersed in a ductile metal matrix in order to obtain characteristics such as hardness and corrosion resistance. Corrosion resistance is one of the important properties of nanocomposites; however, the corrosion mechanism of the Al- SiC nanocomposite has not yet been determined. .In this study, bulk Al-5% SiC nanocomposite was prepared using mechanical alloying and the hot press method. Corrosion behavior was then investigated using EIS techniques such as Nyquist and the Bod diagram. A larger charge transfer resistance was found for the Al- SiC nanocomposite by the EIS diagrams, confirming its corrosion resistance in a 3.5wt% NaCl solution.

Abstract: Ultrasound based inspection techniques are used extensively throughout industry for detection of flaws in engineering materials. The range and variety of imperfections encountered is large and critical assessment of location, size, orientation and type is often difficult. The research presented in this paper has resulted in a knowledge-based engineering module, which was developed software for determining ultrasonic probe location precisely and detecting of the welded sections completely. The criteria for diagnosing these positions, which have been classified into different groups, included in type of material, thickness, geometry of welded section, couplant material, angle probes and etc. The expert system can display the limits that probe must be moved which caused an inspection welded section thoroughly. This study was conducted using three samples including different materials with V groove welded sections for verifying this expert system. Finally this module is very suitable in Q.C. labs and different industries for detection of flaws.