R.K. Dube - Academia.edu (original) (raw)

Papers by R.K. Dube

Intermetallics, 2013

A relatively simple yet attractive and efficient powder metallurgy processing method, based on me... more A relatively simple yet attractive and efficient powder metallurgy processing method, based on mechanical milling and spark plasma sintering of PREP (Plasma Rotating Electrode Processed) pre-alloyed powders, has been proposed to prepare full density fine-grained Ti-rich TieAl alloys with controlled microstructure. Full density fine-grained Ti-rich TieAl alloy compacts, with grain size in the range of 2e4 mm, were successfully prepared from dendritic coarse PREP pre-alloyed powders, which are otherwise difficult to consolidate, by mechanical milling followed by spark plasma sintering at moderate consolidation conditions. It has been demonstrated that the microstructure, i.e. lamellar or equiaxed, depends on the extent of mechanical milling. The fine-grained TieAl compacts exhibited extremely good mechanical properties. An attempt has been made to correlate the effect of mechanical milling on the microstructure and properties of the sintered TieAl compacts.

Gold has fascinated the mankind worldwide, and India is no exception. In fact, India has a very o... more Gold has fascinated the mankind worldwide, and India is no exception. In fact, India has a very old and rich history of gold. In the present paper, various aspects of the history and metallurgy of gold in India from the earliest times till the beginning of the Christian era on the basis of literary evidences have been discussed. It has been shown that India had an abundance of gold right from the beginning of the Ugvedic age. Various aspects of mining, extraction, refining, melting and fabrication were known to people, and these are discussed. A novel variety of gold powder known as Pip~lika or Ants’ gold as described in the great epic Mah’bh’rata has also been discussed. Suvar=abh@mi and Suvar=adv~pa were a sort of El Dorado for the traders and explorers in ancient India. It has been shown that gold was brought to India from these places in the ancient time.

Powder Metallurgy, 1995

AbstractPreparation of fully dense copper strip from Cu2O powder via an integrated powder technol... more AbstractPreparation of fully dense copper strip from Cu2O powder via an integrated powder technology route is briefly described. Full density strip obtained by such a route has been found to contain 0·5 vol.-% of Cu2O inclusions, a somewhat higher level than that found in strip prepared from atomised copper powder. Internal degradation of full density PM copper strip by inclusion-matrix decohesion and/or inclusion fragmentation during cold rolling has been studied as a function of thickness reduction. Coarse inclusions ≥10 μm in size undergo fragmentation/decohesion at relatively small thickness reductions of the order of 20%.In contrast, smaller inclusions in the submicrometre range do not exhibit decohesion/fragmentation after thickness reductions of as high as 60%. Cold rolling thickness reductions up to 20 and 40% were found to be safe for strip prepared from Cu2O and atomised copper powders respectively. For strip produced from Cu2O powder and cold rolled to 20% thickness reduction an annealing treat...

Metallurgical and Materials Transactions A, 2008

A bulk nanocrystalline 80Ni-15Fe-5Co (wt pct) soft magnetic material was successfully pro-duced v... more A bulk nanocrystalline 80Ni-15Fe-5Co (wt pct) soft magnetic material was successfully pro-duced via ''mechanical alloying-explosive compaction'' route. A rapid grain refining was observed during initial 12 hours of milling in high-energy planetary ball mill, followed by a level-off trend. A ...

Metals Technology

AbstractMagnetite superconcentrate powder bonded into strip form was reduced at three different t... more AbstractMagnetite superconcentrate powder bonded into strip form was reduced at three different temperatures. Complete reduction of the strip was achieved at 1200°C resulting in a sponge iron strip containing about 75% porosity. It was found that the sponge iron strip could be hot rolled at 1130° C to a fully dense strip without significant edge cracking. In the initial stages of hot rolling, densification of the strip was brought about mainly by the physical movement of the sponge iron particles in the thickness direction. In the later stages of hot rolling strain was produced in the strip both in the thickness and longitudinal directions, and the sponge iron particles joined together to form a sinuous configuration. Plastic deformation subsequently became the main densification mechanism. A fine-grained strip having an ultimate tensile strength of about 300 MN m−2 coupled with an elongation of about 30% was obtained after a limited amount of hot rolling.

Metallurgical and Materials …, 2010

The present work deals with the preparation of near-full density Cu-Al-Ni shape memory alloy (SMA... more The present work deals with the preparation of near-full density Cu-Al-Ni shape memory alloy (SMA) strips from argon-atomized prealloyed powder via a powder metallurgy (PM) route comprising cold die compaction to prepare powder preforms, sintering, and hot densification rolling of unsheathed sintered powder preforms under protective atmosphere at 1273 K (1000°C). It has been shown that argon-atomized spherical Cu-Al-Ni SMA powder consisted of very fine equiaxed grains and no appreciable grain growth occurred during sintering at 1273 K (1000°C). It also has been shown that no appreciable densification occurred during sintering, and densification was primarily achieved by hot rolling. The densification behavior of the sintered powder preforms during hot rolling was discussed. The hot-rolled Cu-Al-Ni strips were heat-treated at 1223 K (950°C) for 60 minutes and water quenched. The heat-treated strips consisted of equiaxed grains with average size approximately 90 lm. The heat-treated Cu-Al-Ni

British Corrosion Journal, 1996

Abstract Powder metallurgy (PM) sintered iron compacts having 2-9% porosity, and full density PM ... more Abstract Powder metallurgy (PM) sintered iron compacts having 2-9% porosity, and full density PM iron strip were electro less coated successfully with nickel-phosphorus alloy from baths containing sodium hypophosphite. Corrosion behaviour of such specimens in l·0M HCl was investigated. It was shown that anodic and cathodic polarisation plots of such PM iron specimens, irrespective of substrate porosity exhibit Tafel behaviour. Corrosion rates of PM iron compacts of 2-9% porosity and full density strip coated with electro less nickelphosphorus alloy for shorter periods, of the order of 0·5 h increase with substrate porosity. However, the corrosion rate of such PM iron compacts and strip coated for more than 0·5 h, first increases with substrate porosity and then remains practically constant.

Metallurgical transactions. A, Physical metallurgy and materials science, 1993

The relationships between the longitudinal and thickness strains and between the apparent plastic... more The relationships between the longitudinal and thickness strains and between the apparent plastic Poisson's ratio and the relative density achieved during hot rolling of porous nickel strips of initial relative densities 0.36, 0.48, and 0.67 are experimentally determined. The experimental data have been found to agree well with the results predicted from analytical relationships. Hot rolling of such porous metal strips can be divided into three distinct stages. In stage I, the powder particles rearrange and restack as the rolling progresses and the longitudinal elongation and apparent plastic Poisson's ratio are negligibly low. The end of this stage is marked by the situation when no further densification without longitudinal flow is possible by hot rolling

India has a very old and fascinating history of gold. Various aspects of the mining and metallurg... more India has a very old and fascinating history of gold. Various aspects of the mining and metallurgy of gold were known to the Indians since time immemorial. In this paper, different types of the gold ore deposits', and the technique used in the extraction and refining of gold in ancient India as obtained from the literary sources 'composed in the pre-Christian era and some archa-eological findings are discussed. The recovery of a novel variety of high purity gold powder, known as Pipilaka Gold, from the auriferous soil of ant-hills, as stated in the Maheibharata, has also been discussed.

Materials Characterization

Development of characterization tests for ascertaining the purity of precious metals was an impor... more Development of characterization tests for ascertaining the purity of precious metals was an important task and skill in antiquity. The statement of Kau·tilya (Fourth century B.C.) on the characteristic features of pure silver is presented and discussed. According to Kau·tilya, if the cast silver pieces or ingots are of white colour like that of coagulated milk or curd, and have projections similar to a cock's comb on its surface, it should be considered as pure. It has been shown that the projections formed on the surface of cast pure silver are due to the evolution of dissolved oxygen during the solidification of the air-melted silver. The results of macro- and microscopic examinations of a cast pure silver surface are also presented, showing the observation made by Kau·tilya.

Journal of Alloys and Compounds

Recently Cu-Al-Ni shape memory alloys have gained special attention due to their high temperature... more Recently Cu-Al-Ni shape memory alloys have gained special attention due to their high temperature applications. This article attempts to formulate the various processing routes for processing of Cu-Al-Ni shape memory alloys such as casting route, powder metallurgy route, rapid solidification and spray forming process. The pros and cons of various processes are provided in detail. The additive manufacturing, which is an emerging process is discussed which could be a promising technique of preparing Cu-Al-Ni shape memory alloys. Further recommendations are provided in terms of producing fine-grained near net shaped shape memory alloys for high temperature applications.

Metals Technology

Steel strip was produced from iron oxide superconcentrate and the effects of cold rolling (15–50%... more Steel strip was produced from iron oxide superconcentrate and the effects of cold rolling (15–50%) and annealing (500°–700°C for 5–90 min in H2) were investigated by measuring changes in UTS, elong...

Metals Technology

AbstractA technique for producing steel strip from organically bonded iron oxide superconcentrate... more AbstractA technique for producing steel strip from organically bonded iron oxide superconcentrate by a direct route involving hot and cold rolling has already been established. The present paper deals with the structure and properties of the cold-rolled and annealed strip, and compares them with those of conventional materials. The structure of the direct strip is entirely different from that of conventional material and consists of a pure iron matrix containing a high proportion of finely divided impurity inclusions, uniformly distributed. Special consideration is given to the size range and distribution of the inclusions, and to the drawing properties of strip.

Materials Science and Technology

AbstractThe densification of porous copper strips obtained from the combined reduction and sinter... more AbstractThe densification of porous copper strips obtained from the combined reduction and sintering of cuprous oxide preforms by cold rolling has been discussed. It has been shown that such strips, although containing a relatively large amount of porosity, exhibit no problems during cold rolling and, in general, have good workability. Although it is possible to subject the strip to cold rolling thickness deformations of the order of 75%, without any intermediate annealing, rolling with annealing after every 35–40% cold rolling reduction yields better results. The efficiency of densification and changes in the pore morphology during the cold rolling of the porous strip have also been discussed.MST/670

Intermetallics, 2013

A relatively simple yet attractive and efficient powder metallurgy processing method, based on me... more A relatively simple yet attractive and efficient powder metallurgy processing method, based on mechanical milling and spark plasma sintering of PREP (Plasma Rotating Electrode Processed) pre-alloyed powders, has been proposed to prepare full density fine-grained Ti-rich TieAl alloys with controlled microstructure. Full density fine-grained Ti-rich TieAl alloy compacts, with grain size in the range of 2e4 mm, were successfully prepared from dendritic coarse PREP pre-alloyed powders, which are otherwise difficult to consolidate, by mechanical milling followed by spark plasma sintering at moderate consolidation conditions. It has been demonstrated that the microstructure, i.e. lamellar or equiaxed, depends on the extent of mechanical milling. The fine-grained TieAl compacts exhibited extremely good mechanical properties. An attempt has been made to correlate the effect of mechanical milling on the microstructure and properties of the sintered TieAl compacts.

Gold has fascinated the mankind worldwide, and India is no exception. In fact, India has a very o... more Gold has fascinated the mankind worldwide, and India is no exception. In fact, India has a very old and rich history of gold. In the present paper, various aspects of the history and metallurgy of gold in India from the earliest times till the beginning of the Christian era on the basis of literary evidences have been discussed. It has been shown that India had an abundance of gold right from the beginning of the Ugvedic age. Various aspects of mining, extraction, refining, melting and fabrication were known to people, and these are discussed. A novel variety of gold powder known as Pip~lika or Ants’ gold as described in the great epic Mah’bh’rata has also been discussed. Suvar=abh@mi and Suvar=adv~pa were a sort of El Dorado for the traders and explorers in ancient India. It has been shown that gold was brought to India from these places in the ancient time.

Powder Metallurgy, 1995

AbstractPreparation of fully dense copper strip from Cu2O powder via an integrated powder technol... more AbstractPreparation of fully dense copper strip from Cu2O powder via an integrated powder technology route is briefly described. Full density strip obtained by such a route has been found to contain 0·5 vol.-% of Cu2O inclusions, a somewhat higher level than that found in strip prepared from atomised copper powder. Internal degradation of full density PM copper strip by inclusion-matrix decohesion and/or inclusion fragmentation during cold rolling has been studied as a function of thickness reduction. Coarse inclusions ≥10 μm in size undergo fragmentation/decohesion at relatively small thickness reductions of the order of 20%.In contrast, smaller inclusions in the submicrometre range do not exhibit decohesion/fragmentation after thickness reductions of as high as 60%. Cold rolling thickness reductions up to 20 and 40% were found to be safe for strip prepared from Cu2O and atomised copper powders respectively. For strip produced from Cu2O powder and cold rolled to 20% thickness reduction an annealing treat...

Metallurgical and Materials Transactions A, 2008

A bulk nanocrystalline 80Ni-15Fe-5Co (wt pct) soft magnetic material was successfully pro-duced v... more A bulk nanocrystalline 80Ni-15Fe-5Co (wt pct) soft magnetic material was successfully pro-duced via ''mechanical alloying-explosive compaction'' route. A rapid grain refining was observed during initial 12 hours of milling in high-energy planetary ball mill, followed by a level-off trend. A ...

Metals Technology

AbstractMagnetite superconcentrate powder bonded into strip form was reduced at three different t... more AbstractMagnetite superconcentrate powder bonded into strip form was reduced at three different temperatures. Complete reduction of the strip was achieved at 1200°C resulting in a sponge iron strip containing about 75% porosity. It was found that the sponge iron strip could be hot rolled at 1130° C to a fully dense strip without significant edge cracking. In the initial stages of hot rolling, densification of the strip was brought about mainly by the physical movement of the sponge iron particles in the thickness direction. In the later stages of hot rolling strain was produced in the strip both in the thickness and longitudinal directions, and the sponge iron particles joined together to form a sinuous configuration. Plastic deformation subsequently became the main densification mechanism. A fine-grained strip having an ultimate tensile strength of about 300 MN m−2 coupled with an elongation of about 30% was obtained after a limited amount of hot rolling.

Metallurgical and Materials …, 2010

The present work deals with the preparation of near-full density Cu-Al-Ni shape memory alloy (SMA... more The present work deals with the preparation of near-full density Cu-Al-Ni shape memory alloy (SMA) strips from argon-atomized prealloyed powder via a powder metallurgy (PM) route comprising cold die compaction to prepare powder preforms, sintering, and hot densification rolling of unsheathed sintered powder preforms under protective atmosphere at 1273 K (1000°C). It has been shown that argon-atomized spherical Cu-Al-Ni SMA powder consisted of very fine equiaxed grains and no appreciable grain growth occurred during sintering at 1273 K (1000°C). It also has been shown that no appreciable densification occurred during sintering, and densification was primarily achieved by hot rolling. The densification behavior of the sintered powder preforms during hot rolling was discussed. The hot-rolled Cu-Al-Ni strips were heat-treated at 1223 K (950°C) for 60 minutes and water quenched. The heat-treated strips consisted of equiaxed grains with average size approximately 90 lm. The heat-treated Cu-Al-Ni

British Corrosion Journal, 1996

Abstract Powder metallurgy (PM) sintered iron compacts having 2-9% porosity, and full density PM ... more Abstract Powder metallurgy (PM) sintered iron compacts having 2-9% porosity, and full density PM iron strip were electro less coated successfully with nickel-phosphorus alloy from baths containing sodium hypophosphite. Corrosion behaviour of such specimens in l·0M HCl was investigated. It was shown that anodic and cathodic polarisation plots of such PM iron specimens, irrespective of substrate porosity exhibit Tafel behaviour. Corrosion rates of PM iron compacts of 2-9% porosity and full density strip coated with electro less nickelphosphorus alloy for shorter periods, of the order of 0·5 h increase with substrate porosity. However, the corrosion rate of such PM iron compacts and strip coated for more than 0·5 h, first increases with substrate porosity and then remains practically constant.

Metallurgical transactions. A, Physical metallurgy and materials science, 1993

The relationships between the longitudinal and thickness strains and between the apparent plastic... more The relationships between the longitudinal and thickness strains and between the apparent plastic Poisson's ratio and the relative density achieved during hot rolling of porous nickel strips of initial relative densities 0.36, 0.48, and 0.67 are experimentally determined. The experimental data have been found to agree well with the results predicted from analytical relationships. Hot rolling of such porous metal strips can be divided into three distinct stages. In stage I, the powder particles rearrange and restack as the rolling progresses and the longitudinal elongation and apparent plastic Poisson's ratio are negligibly low. The end of this stage is marked by the situation when no further densification without longitudinal flow is possible by hot rolling

India has a very old and fascinating history of gold. Various aspects of the mining and metallurg... more India has a very old and fascinating history of gold. Various aspects of the mining and metallurgy of gold were known to the Indians since time immemorial. In this paper, different types of the gold ore deposits', and the technique used in the extraction and refining of gold in ancient India as obtained from the literary sources 'composed in the pre-Christian era and some archa-eological findings are discussed. The recovery of a novel variety of high purity gold powder, known as Pipilaka Gold, from the auriferous soil of ant-hills, as stated in the Maheibharata, has also been discussed.

Materials Characterization

Development of characterization tests for ascertaining the purity of precious metals was an impor... more Development of characterization tests for ascertaining the purity of precious metals was an important task and skill in antiquity. The statement of Kau·tilya (Fourth century B.C.) on the characteristic features of pure silver is presented and discussed. According to Kau·tilya, if the cast silver pieces or ingots are of white colour like that of coagulated milk or curd, and have projections similar to a cock's comb on its surface, it should be considered as pure. It has been shown that the projections formed on the surface of cast pure silver are due to the evolution of dissolved oxygen during the solidification of the air-melted silver. The results of macro- and microscopic examinations of a cast pure silver surface are also presented, showing the observation made by Kau·tilya.

Journal of Alloys and Compounds

Recently Cu-Al-Ni shape memory alloys have gained special attention due to their high temperature... more Recently Cu-Al-Ni shape memory alloys have gained special attention due to their high temperature applications. This article attempts to formulate the various processing routes for processing of Cu-Al-Ni shape memory alloys such as casting route, powder metallurgy route, rapid solidification and spray forming process. The pros and cons of various processes are provided in detail. The additive manufacturing, which is an emerging process is discussed which could be a promising technique of preparing Cu-Al-Ni shape memory alloys. Further recommendations are provided in terms of producing fine-grained near net shaped shape memory alloys for high temperature applications.

Metals Technology

Steel strip was produced from iron oxide superconcentrate and the effects of cold rolling (15–50%... more Steel strip was produced from iron oxide superconcentrate and the effects of cold rolling (15–50%) and annealing (500°–700°C for 5–90 min in H2) were investigated by measuring changes in UTS, elong...

Metals Technology

AbstractA technique for producing steel strip from organically bonded iron oxide superconcentrate... more AbstractA technique for producing steel strip from organically bonded iron oxide superconcentrate by a direct route involving hot and cold rolling has already been established. The present paper deals with the structure and properties of the cold-rolled and annealed strip, and compares them with those of conventional materials. The structure of the direct strip is entirely different from that of conventional material and consists of a pure iron matrix containing a high proportion of finely divided impurity inclusions, uniformly distributed. Special consideration is given to the size range and distribution of the inclusions, and to the drawing properties of strip.

Materials Science and Technology

AbstractThe densification of porous copper strips obtained from the combined reduction and sinter... more AbstractThe densification of porous copper strips obtained from the combined reduction and sintering of cuprous oxide preforms by cold rolling has been discussed. It has been shown that such strips, although containing a relatively large amount of porosity, exhibit no problems during cold rolling and, in general, have good workability. Although it is possible to subject the strip to cold rolling thickness deformations of the order of 75%, without any intermediate annealing, rolling with annealing after every 35–40% cold rolling reduction yields better results. The efficiency of densification and changes in the pore morphology during the cold rolling of the porous strip have also been discussed.MST/670