Materials Science Forum Vols. 702-703

Abstract: This paper reports the effect of Ho on the microstructure, texture and magnetostrictive properties of Tb_0.3Dy_0.7-xHo_xFe_1.95 (with x = 0, 0.05, 0.1, 0.15 and 0.2) alloys. The alloys were vacuum induction melted and directionally solidified by modified Bridgman technique. Ho addition has been found to improve the magnetostriction at lower concentration due to absence of deleterious pro-peritectic (Tb,Dy)Fe3 phase. The static strain co-efficient is found to be better in Ho added alloys and the prevalence of strong and texture is attributed to be the reason.

Abstract: Aluminium alloys for car body manufacturing often show a specific type of band-shaped surface roughening upon stretching, called “ridging” or “roping”. Experimental research as well as modelling attempts have indicated that the evolving surface roughness profiles cannot be understood based on banding of individual surface texture components, like cube or Goss, only. Therefore, it is proposed to study banding on the “mesoscopic” level of texture banding rather than on the “microscopic” one of orientation banding. In mechanical terms, such patterning in the texture would lead to patterning in, for instance, the Lankford coefficient (r-value), so that the mechanical response can be calculated on an intermediate length scale. The present contribution presents a method for calculating r-value patterning from Electron Backscatter diffraction (EBSD) orientation maps. In a first test case of a strongly ridging AA6xxx sheet, indeed patterning in the r-value is found which corresponds to reported patterning of the surface roughness.

Abstract: In order to form thin metal sleeve with the thickness of 0.03 mm, type 304 austenitic steel sheet was deeply drawn to a cup and spinning method applied to its body. The sleeve shows high strength with a dual-phase microstructure of fine austenite and transformed martensite. Pancaked austenite and martensite grains were highly elongated along RD (drawing direction) in the layer structure, and their grain width was about 100 nm. Dynamically recovered austenite grains were highly aligned from {101} to {101}. The strain-induced martensite grains mainly showed two components of {001} and {111}. Recover and recrystallization of the sleeve appeared at the temperature from 873 K to 1073 K. Annealed at 1073 K the austenite grains were mostly recrystallized with intensifying {101}, and the martensite grains were also reverse-transformed to austenite.

Abstract: Chromium carbide based metal matrix composite (MMC) coatings are ideally suited for high temperature erosive-corrosive applications. Laser cladding of such MMCs, with Inconel as the ductile matrix instead of the usual NiCr alloy, has been attempted in the present study. The relative hardness of the laser clad layers was observed to drop with increase in laser power. The reduction in hardness was attributed to retention of lower amounts of chromium carbides in the clad layer at higher laser powers. Use of chemically assisted scans with electron diffraction allowed extraction of effective micro-textural information on the coatings

Abstract: PVD hard coatings, notably transition metal nitrides and carbides, are being increasingly used by industry for improving the life and machining speeds of cutting and forming tools. There has been an increasing trend towards use of complex coatings, based on ternary and even more complex multi-component systems, as well as in novel configurations such as multilayers, superlattices, nanolayers and graded coatings, to achieve superior properties in the tool as well as the finished product. The service properties of the coatings are known to be influenced by their microstructure, phase assembly and composition, apart from the orientation and stress states which can be suitably tailored for diverse applications. In the present study, a ternary coating based on Titanium Aluminum Nitride was deposited on high speed steel substrates by cathodic arc evaporation under varied bias voltage conditions. As-deposited coatings were characterized by X-ray diffraction, Residual Stress Analysis, Scanning Electron Microscopy (SEM), EBSD and FIB. Mechanical and tribological characteristics of the coatings were evaluated by nanoindentation and nanoscratch testing, respectively. The variations in coating hardness and adhesion with the bias voltage were studied. The changes in coating microstructure as a consequence of variation in bias voltage were also examined. Results from the above investigations are presented to illustrate how a combination of electron microscopy with nanoindentation and adhesion testing can be utilized to ascertain structure-property correlations in coatings.

Abstract: An In-situ Mg-based bulk metallic glass (BMG) composite containing 40% volume fraction of Mg-rich crystalline flakes was produced by die casting. During cooling from the melt, the flakes nucleate heterogeneously and subsequently grow with their broad faces parallel to the {0001} plane. This generated a uniform dispersion of randomly-oriented flakes within an amorphous matrix. When compressed uniaxially up to 60% reduction in the supercooled liquid (SCL) region, the flakes in this composite were substantially aligned their broad faces towards the compression plane that generated a strong //ND fibre texture.

Abstract: In the present study ultrasonic vibrations are used for the grain refinement of AZ91 alloy during its solidification. The microstructures and mechanical properties of the treated AZ91 alloy are characterized. It is found that due to the acoustic cavitation and flows induced by ultrasonic vibration during the nucleation stage, the formation of the fine uniform globular grains are attributed to the combination of the enhanced heterogeneous nucleation and dendrite fragmentation. The average grain size decreases with increase in ultrasonic intensity but the largest reduction occurs mainly from 1.34KW/cm2 to 2.69K W/cm2; the benefits of further increase in the ultrasonic intensity from 2.69KW/cm2 to 4.031KW/cm2 are small.

Abstract: This study describes the influence of texture and associated mechanical properties on ballistic performance of Aluminium-7017 alloy in two different (unidirectional and clock) hot rolling conditions. The change in texture has been explained in terms of β fiber in hot rolled and T6 tempered condition. A marginal variation in strength and hardness is observed with changing the mode of rolling, whereas Charpy impact values are found to be varying considerably. Results show that the unidirectional rolled material exhibits improved ballistic performance than that of the clock rolled plate. This has been attributed to different textures present in both the plates.

Abstract: Present work describes the evolution of texture during different modes of deformation by cold rolling of a Gum metal or multifunctional β titanium alloy. The starting and cold rolled materials exhibit the presence of β and β with small amount of stress induced martensitic (α˝) phases, respectively. The development of texture has been explained in terms of α and γ fibres. The bulk hardness appears to be independent of modes of deformation by cold rolling. The yield surfaces of as received and solution treated samples exhibit marked anisotropy which persists during different modes of deformation by rolling.

Abstract: Present work describes the development of texture in high purity aluminum under different modes of deformation by rolling using two different roll diameters, namely 300 and 610 mm. It has been observed that the change in both the roll diameter as well as the modes of rolling has a marked influence on the evolution of texture as well as the characteristics of a- and β-fibres. The results are discussed in terms of the effects of roll gap geometry and the relevant stress conditions that affect the strain path of crystallite rotation.