Vipin Kant Singh

Dependence of strain hardening exponent on the volume fraction and carbon content of martensite in dual phase steels during multistage work hardening

This letter deals with the influence of volume fraction (V m ) and carbon content (C m ) of martensite in ferrite-martensite dual phase steels on the value of n for different stages of strain hardening. This particular aspect has not so far been systematically investigated and reported in the literature

On the fracture characteristics of leaded aluminium alloys

Aluminium alloys with proper distribution of lead have high potential as materials for plain bearings. In fact, lead has been found to be either equivalent to or even more effective than tin as a soft phase alloying addition [1] in aluminium and its alloys. However, some unfavourable factors, such as the wide miscibility gap, large range of solidification and high disparity in the densities of aluminium and lead, cause practical problems in preparation of aluminium-lead alloys with a uniform distribution of lead. Pathak et al. [2] successfully demonstrated, using an improved design of impeller mixer and a modified technique of chill casting, that a fairly uniform distribution of lead up to 50 wt % can be obtained in aluminium and its alloys. The microstructures and mechanical properties of the aluminium-lead alloys, with varying lead content from 5 to 50 wt % are reported elsewhere [2, 3]. Ichikawa and Ishizuka [4] prepared leaded aluminium alloys with varying lead content from 5 to 50 wt % by rheocasting. They selected the same base alloys that were studied by the previous investigators [2, 3] and reported an improvement in tensile strength but a reduction in ductility of leaded aluminium alloys at room temperature, and Mohan et al. [5] prepared aluminium-lead alloys by stir casting and found a uniform distribution of lead both in longitudinal as well as transverse sections of the ingot castings. This letter is concerned with the effect of lead content on the fracture characteristics of aluminium-lead ingot castings tested in tension at room temperature. Commercially pure aluminium (99.5% purity) and lead (99.9% purity) were obtained from the Indian Standards Company, Bombay. Aluminium-lead alloys with lead content of 5-50 wt % were prepared, using an especially designed impeller for mixing and the technique of bottom discharge chill casting [2, 6]. The specimens for optical microscopy were mechanically polished and etched by Kellers reagent. Cylindrical Hounsfield tensile specimens with gauge diameter of 4.5 mm and gauge length of 16 mm were machined from the cast ingots. Tensile tests were conducted at room temperature using a servomechanical Instron machine at a crosshead speed of 2 mmmin -t. The fracture surfaces were examined by a Philips scanning electron microscope PS EM500. The tensile properties of the commercial purity aluminium, lead and the lead alloys are recorded in Table I. It may be seen that whereas the strength parameters decrease, the ductility parameters increase with the lead content. These variations in the properties of the aluminiumlead alloys may be attributed to the soft and ductile nature of lead. It may be noted that whereas the effect of lead on the ductility is high up to 25 wt % Pb, its effectiveness decreases at higher lead content. Hence, the fracture behaviour of only two alloys, one with 15 wt% Pb and the other with 45 wt % Pb is discussed. The optical micrographs in Fig. la and b show the size, shape and distribution of the lead-rich phase (dark etching) in the aluminium-rich matrix. It may be seen that average thickness of the lead-rich pockets is considerably higher in the A1-45 wt % Pb than that in the A1-15 wt% Pb. The scanning electron micrographs in Fig. 2 show the fracture characteristics of the A1-15 wt% Pb. The dark regions with irregular shape in the scanning electron micrographs (Fig. 2a) are depressions arising from the lead-rich regions. The lead-rich aggregates appear to have undergone extensive plastic deformation (Fig. 2b). In addition, there are two types of dimples, one with dark and the other with light contrast. The dimples are mostly equiaxed. The dark dimples are due to the lead-rich constituent and the

Effect of lead content on tensile fracture of Al-4.5Cu-Pb bearing alloy

A1-4.5% Cu alloys containing lead have been characterized and advocated for use as plain.bearing materials. These alloys posses not only the requisite strength [1-3] but also good friction and wear resistance [3-5]. It has been established [5-7] that the lead in aluminium alloys acts as a lubricant and reduces the friction and wear between the mating surfaces. The effect of lead on mechanical [1, 2] and tribological [4, 5, 8] properties of aluminium alloys has been reported in detail, but the role of lead on the fracture characteristics has not been examined. Pathak et al. [9] recently studied the fracture characteristics of aluminium, containing various amounts of lead, tested under tension at room temperature. They established that although at low lead content fracture occurs due to the nucleation, growth and coalescence of voids at lead particles, failure of specimens with high lead content occurs from extensive fragmentation of the coarse lead aggregates. This letter is concerned with the characterization of the tensile fracture of A1-4.5% Cu alloy with various lead contents from 10 to 40 wt %. Cylindrical castings of A1-4.5% Cu with 10-40 wt % lead, with length 150 mm and diameter 25 mm, were prepared by impeller mixing and bottom-discharge chill casting [10]. Honsfield tensile specimens with gauge length 16 mm and gauge diameter 4.5 mm were machined from the ingot castings and tested at room temperature using an Instron universal testing machine at a crosshead speed of 2mmmin -1. The fracture surfaces were examined using a Philips PSEM 500 scanning electron microscope. The optical micrograph in Fig. 1 shows the microstructure of the specimen with Pb content 40 wt %. It can be seen that there is fairly uniform dispersion of lead even at high lead content. The tensile properties of the A1-4.5% Cu alloy with various Pb contents are given in Table I. It may be

Hydration and some other Properties of CA, CA2 and their Mixes

CA, CA2 and their mixes with and without alumina aggregate were allowed to hydrate below 25°C and in not less than 90% relative humidity. The various phases formed were determined by X-ray analysis. The data obtained showed that the hydration products of CA were C3AH6 and AH3 whereas CA2, CA—CA2 mixes gave higher percentage of CAH10 and AH3. Hydrated CA mixes with Al2O3 after firing gave CA2 and CA6, whereas CA—CA2 mixes gave CA6. The strength value of CA—CA2 mixes increased with increase in CA2 content whereas PCE value increased with increase in CA2 content.

Sintering of Alumina in the Presence of Liquid Phase

Sintering of alumina has been carried out in presence of two eutectic glass compositions, viz. CAS (1): CaO–23.0, Al2O3–15.0, SiO2–62.0 and CAS (2): CaO–52.0, Al2O3–41.5, SiO2–6.5. 10, 15, 20 and 25 per cent by weight glass were used with different particle sizes of Al2O3 and sintered at 1400° and 1460°C. Effect of particle size of Al2O3 and glass content were studied from isothermal density variation. It was found that CAS(2) glass was more effective in promoting sintering of Al2O3 than CAS (1).

Liquid Phase Sintering of Silica

SiO2 has been sintered in the presence of a silicate liquid containing CaO 23%, AlO2O3 15% and SiO2, 62%. Silicon dioxide powders of -45 and -75 + 63 micron particle sizes were taken and sintered with 10, 15 and 20% by weight liquid phase. Sintering temperatures were 1250°, 1300°, 1350° and 1400°C and soaking periods were from 1 to 30 minutes. Effects of liquid content of the compact and the sintering temperature were studied for the two particle sizes of SiO2. Data were analysed using the empirical equation D = K log t + C and Arrhenius equation. It was found that activation energy of sintering decreased with the increasing amount of liquid phase and -45 micron SiO2 sintered with much faster rate than -75+63 micron.

Studies on the Workability of Cement-Lime-Sand Mortars

Workability of cement, lime and sand mortars was studied by the measurement of flow on a flow table. Effects of cement and sand proportions were investigated by taking various mixes from 1:1.0 to 1:5.0 cement: sand mortars. 1:2.5, 1:3.0 and 1:3.5 cement: sand mixes were further studied by the use of lime as workability aid.It was found that mixes of cement and sand from 1:1.0 to 1:4.0 ratio behave like plastic masses and workability increases by increase in water content without any yield point. 1:4.5 and 1:5.0 cement: sand mixes gave certain yield values. Overall workability of various mixes with different water content has shown that workability increases from 1:1.0 to 1:2.0 and thereafter it decreases from 1:2.5 to 1:5.0 cement: sand mixes. The effect of lime was that it increases the workability in each case and the effect is more marked at higher lime contents in the mixes.

Studies on the Sintering of Silicon Dioxide

Sintering studies were carried out on SiO2 by taking compacts of different particle sizes of double calcined silicon dioxide. Effects of particle size, sintering temperature and sintering time were investigated. The data were analysed using the empirical equation D = K log t + C. It was observed that the activation energy for sintering of SiO2 increases with increase in particle size from −45 μ to −106+90 μ powder.

Studies on the Sintering of Tricalcium Aluminate

Sintering studies were carried out on tricalcium aluminate prepared by solid-solid reaction between calcium carbonate and aluminium oxide. Effects of forming pressure, particle size, sintering temperature and sintering time were investigated. The data were analysed using the empirical equation D = K log t+C.It was observed that the activation energy for the later stage of sintering increases with particle size from-53+45μto-75+63μ. Increase in compaction pressure, sintering temperature and use of multisized particles gave nearly theoretical density.

SINTERING OF CALCIUM ALUMINATE

Measurements of initial sintering shrinkage of CaAl4O7are reported in the temperature range 1380°-1480°C. The particle size chosen was—45 micron and the soaking periods were from 10 to 180 minutes. The time dependance of shrinkage indicated that the grain boundary diffusion is the dominant mechanism of sintering. The activation energy for the sintering of CaAl4O7 was found to be 151.0 k cal.mol−1.