Showing papers by "Defence Metallurgical Research Laboratory published in 1982"

An investigation of pack-aluminide coating on steel

Abstract: Aluminide coatings are known to protect steels from oxidation and corrosion in hydrocarbon and sulfur-bearing atmospheres. Pack cementation is ideally suited for forming these coatings on small intricate components, wherein a diffused layer is formed which is well bonded to the substrate. Even though pack aluminide coated steels are being commercially used, there has not been any systematic investigation of the factors that control the coating formation. The present investigation has been carried out to define the boundary conditions under which diffusion in the solid phase determine the coating kinetics. The effect of pack activity and temperature on the structure and kinetics of aluminde layer formation on EN-3 steel has been investigated. The coating characteristics were evaluated by metallography, EPMA, X-ray diffraction, and scanning electron microscope (SEM). Oxidation resistance of the coated samples were compared to that of 304 stainless steel after heating in air at 900°C for 72 h. The surface aluminum composition was found to be about 20% by weight which remained constant with time in the temperature range of 750°C–900°C. Weight gains and layer thicknesses obeyed parabolic relationship with time at all temperatures. Under these conditions, the system constitutes a vapor-solid diffusion couple. Interdiffusion coefficient\((\tilde D)\)values in the Fe-Al system have been determined, and the activation energy has been calculated to be 57 Kcals/mole, which agrees well with the literature values.

An evaluation study of aluminide and chromoaluminide coatings on IN-100

Abstract: Aluminide diffusion coatings are commonly used to protect aircraft gas turbine blades and vanes from oxidation and hot-corrosion attack. These coatings are based on NiAl intermetallic compound with other alloying elements like Cr and Ti either diffused from the superalloy substrate or incorporated in a separate coating step. The present investigation is mainly concerned with the development of both aluminide and chromoaluminide coatings on IN-100, a cast Ni-base superalloy. The coating structure and composition have been characterized and the cyclic oxidation and hot corrosion properties have been evaluated for the different types of coatings. The difference in the hot-corrosion properties between the aluminide and the chromoaluminide coatings has been rationalized in terms of the coating chemistry. The mode of coating degradation under hot-corrosion conditions has also been analyzed.

Diffusitivity of carbon in Fe-V alloys

Abstract: Tracer diffusion of carbon in iron—vanadium alloys containing 2.45, 0.5 and 0.1 at% vanadium has been measured in a temperature range from 900 to 1325 K. No effect of magnetic transforms is observed on the C14 diffusivity in the α-stabilized Fe-2.4 at% V alloy, as has been reported for α-iron. Trapping behaviour of vanadium in slowing down the carbon diffusivity in iron shows a reasonable fit with the model predicted by Koiwa. However, the effect of these traps appears not to be felt during lowtemperature internal friction measurements in Fe-2.4 at% V alloy.

Eutectic growth in space

Abstract: Defect-free eutectic components are favoured for certain applications in view of their improved performance and/or better stability Eutectics produced even under best conditions possible on earth have some microstructural defects Unavoidable density driven convectional currents in liquid are considered as a major cause for the production of these defects Intensity of such convectional currents proportionally reduces with gravity Therefore the defect density in the eutectics is expected to be very low when processed under microgravity conditions The advantages and limitations of processing under microgravity conditions are examined The potential of newly developed ‘skin technology’ for processing eutectic components in space is considered

Dispersion Hardening of Titanium

Abstract: The strengthening of titanium and beta III alloy by dispersions of ceria, yttria and misch metal oxides is investigated. The oxides were incorporated in the matrix by internal oxidation. The warm-rolled strips of these materials were annealed at high temperatures. The recovery of the mechanical properties and microstructure were followed by hardness and tensile testing and by optical and electron microscopy. These studies revealed that whilst the dispersoids do not prevent recrystallization, they hinder grain growth. High temperature tensile tests indicate that increase in strength brought about by dispersoids is temperature dependent and falls off above 600°C.

Thermal-Expansion Studies of High-Damping Mn-Cu Alloys

Abstract: The thermal expansion of Mn-Cu alloys was measured in order to study the phase transformation and to assess the stability of the phases responsible for the high damping capacity observed in these alloys. High internal stresses build up during these transformations, and a large volume contraction could provide the necessary mechanism for absorption of vibrational energy.

Critical Review Powder Metallurgy of Titanium

Abstract: Powder metallurgy offers an attractive alternate strategy for producing titanium parts. The advantages include an efficient material utilization, near-net shape products with better mechanical properties. It is not without significance that the initial pioneering experiments by the U.S. Bureau of Mines were first in producing titanium powder compacts. Interstitial pick-up encountered during reduction prevented the exploitation of the powder route. Early experiments on the production of titanium powder during the metal reduction stage itself were carried out in the Soviet Union using the calcium hydride process. These efforts were only marginally successful because of impurity pick-up during reduction. More than anything else, non-availability of a good quality powder is responsible for titanium powder metallurgy remaining dormant for a number of years.