17 March 1995
FROM: Capt Paul McQuay
AFOSR/AOARD
US Address: Unit 45002, APO AP 96337-0007
Int'l Address: 7-23-17 Roppongi, Minato-ku, Tokyo 106, Japan
Tel/Fax: +81 (3) 5410-4409/4407
SUBJECT: Liaison Report - Summary of Visit to the Bhabha Atomic Research Center (BARC), Bombay, India, 15 Nov 94
ABSTRACT
This Liaison Report summarizes my visit to the Bhabha Atomic Research Center (BARC), Bombay, India, on 15 Nov 94. BARC serves as the principal R&D;center for the Indian Atomic Energy Commission. They are very well equipped and staffed in the area of materials science, especially in physical metallurgy, extractive and chemical metallurgy, and materials joining. In these areas especially, there are several programs which should be of interest to the aerospace materials R&D;community.
VISIT SUMMARY
My visit to BARC was a result of a long-standing invitation from Dr. S. Banerjee, Head of the Metallurgy Division, and Dr. R.V. Ramanujan also of the Metallurgy Division. Unfortunately, Dr. Banerjee was out of town, and Dr. Ramanujan was in the US during my visit, so I was hosted by Dr. C.K. Gupta, Director of the Materials Group. The full list of contacts at BARC are listed in Appendix 1.
BARC is the primary R&D;center for nuclear energy in India. The metallurgy division at BARC is staffed by approximately 130 scientists and engineers. The metallurgy division is comprised of the following sections: High Temperature Materials; Chemical Metallurgy; Metallurgical Thermochemistry; Physical Metallurgy; Mechanical Metallurgy; Corrosion Metallurgy; Electrochemical Science and Technology; Ceramic Science; Ceramics Technology; Process Engineering; and Fabrication and Maintenance.
Dr. Bannerjee's group hosted the International Conference on Advances in Physical Metallurgy - 94 at BARC, 9-11 Mar 94. The conference was reportedly well attended and received by leading scientists from the US, Europe, Japan and of course India.
In addition to the expected R&D;on steels, nickel and zirconium alloys, there are also research programs studying structural intermetallics and ceramics, diamond synthesis by HFCVD, materials under the influence of high hydrostatic and non-hydrostatic stress, bonding and joining of dissimilar materials, oxidation and corrosion behaviour, shape memory alloys, and quasicrystalline alloys.
In particular some of the research investigating techniques to join dissimilar metals/materials should be of interest to the aerospace community. They have successfully bonded Zircaloy2/SS, Ti/SS, Ti/TiAl and various metal/ceramic systems via diffusion bonding with the aid of interlayer materials to manage chemical and mechanical interfacial incompatibilities.
They also have conducted studies examining the kinetics of phase transformations and development of microstructure in many intermetallic systems of interest, including TiAl, Nb3Al, Ni3V, etc.
Several selected extended abstracts from a recent BARC publication are given in Appendix 2, which gives a flavor for some of the aerospace applicable research being conducted at BARC.----------------------------
APPENDIX 1
POINTS OF CONTACT AT BARC
Dr. C.K. Gupta
Director
Materials Group
Bhabha Atomic Research Centre
Trombay-Bombay, 400 085
Tel/Fax: +91 (22) 556-0750/556-0750
Dr. S. Banerjee
Head
Metallurgy Division
Bhabha Atomic Research Centre
Trombay-Bombay, 400 085
Tel/Fax: +91 (22) 551-9949/556-0534
Dr. Raju Ramanujan
Scientific Officer
Metallurgy Division
Bhabha Atomic Research Center
Bombay, 400 085
Tel/Fax: 91-022-556-3060/0750
Dr. U.K. Chaterjee
Head, Laser and Plasma Technology Division
Bhabha Atomic Research Center
Bombay, 400 085
Tel: 91-022-551-9947
Dr. M. Sundararaman
Scientific Officer
Metallurgy Division
Bhabha Atomic Research Center
Bombay, 400 085
Tel/Fax: 91-022-556-3060/0750
Dr. M.K. Totlani
Head, Electrochemical Science and Technology Section
Bhabha Atomic Research Centre
Metallurgy Division
Bombay, 400 085/0750---------------------------
APPENDIX 2
EXCERPTED ABSTRACTS FORM BARC PUBLICATION, "CURRENT PROGRAMMES ON PHYSICAL METALLURGY AND RELATED AREAS IN BARC," 1994.
THEORETICAL STUDY OF ALLOY PHASE STABILITY
A. Arya, G.P. Das and S. Banerjee
Metallurgy Division, Solid State Physics Division,
Bhabha Atomic Centre, Bombay 400085
Ab initio investigation of the stable and metastable phases of binary alloys has been an active and challenging area. The aim is to have a microscopic understanding of the order-disorder transformation, occurrence of spinodal clustering and the ordering process, phase diagram and other thermodynamic properties. In order to get a reliable theoretical estimate of the free energy as a function of temperature (T), concentration (c), and order parameter (both long range (h) and short range (a)), we deploy the highly efficient and reasonably accurate tight-binding linearized muffin-tin orbital (TB-I, MTO) method for the ground state total energy calculations.
The volume dependent effective cluster interactions have been obtained from the total energies of the ordered stoichiometric phases, using Connolly-Williams prescription. The configurational entropy has been calculated using the most accurate mean field method viz. the Cluster Variation Method (CVM). Our results obtained for Lithium Aluminum alloys (see fig. 1 for the predicted heats of formation) are in very good agreement with other state of the art local density calculations and also with the available experimental data Further works on transition-metal alloys are in progress.-------------------------------------
QUASICRYSTALLINE ALLOYS
G.K. Dey, R.T. Savalia, U.D. Kulkarni and S. Banerjee
Metallurgy Division
The melt spinning facility available in the Metallurgy Division has been utilised to produce quasicrystalline alloys in a very large number of alloy systems. The primary aim of these studies have been to identify new quasicrystal forming compositions and to generate phases which are similar in structure to the quasicrystalline phases but are periodic. In the quest for new quasicrystal forming alloys, one of the prominent guidelines is the structure of the alloy in its equilibrium crystalline state. Presence of icosahedral clusters in the equilibrium crystalline state is a positive indication that a particular alloy may yield quasicrystal on rapid solidification. With this point in view several alloy systems have been selected for examining the possibility of quasicrystal formation on rapid solidification. Important among these are alloys from the following alloy systems - Mg-Cu-Al, Mg-AI-Zn and Al-Cu-Fe. In some of these alloys, the decomposition of the rapidly solidified microstructure has also been examined.
The important observations made in the aforementioned studies and the conclusions following these observations are briefly discussed here.
Mg-AI-Zn : A low symmetry derivative of the icosahedral phase forms on rapid solidification in the binary. alloy Mg32Al49. Microstructure of this phase is quite similar to the icosahedral phase in ternary Mg-AI-Zn alloys. A negligibly small amount of the icosahedral phase forms in the Zn rich alloy Mg32Al7Zn42- crystalline MgZn2 constitutes the bulk of this RSP alloy. Substantial amounts of the icosahedral phase form in the alloys with intermediate [Al]/[Zn] ratio (i.e. in Mg32Al24.5Zn24.5 and M932AI17Zn32 alloys). The [Al]/[Zn] ratio also determines the nature of the second phase present in these alloys. The icosahedral phases encountered in this series of alloys in this alloy system show considerable departure from ideal icosahedral diffraction symmetry, the extent of distortion being a function of the [Al]/[Zn] ratio. Although the grains of the icosahedral and the near-icosahedral phases observed in this study showed a particle-like contrast and sectorial division, microdiffraction evidence indicated the presence of a single phase. Though rapid solidification of the binary Mg32Al49 alloy leads to the formation of a low symmetry derivative of the icosahedral phase, addition of a very small amount of Zn (~ 6.5 at %) can transform the microstructure to a completely quasicrystalline
structure. In the alloy Mg32Al34Zn15, the presence of T phase could be detected in the rapidly solidified microstructure. The observed structure of the T-phase forming on rapid solidification was found to be similar to that of T-Mg32AIZn)49,
Al-Cu-Fe system: The alloy Al23CuFe4 was chosen for exploring the possibility of quasicrystal formation since the equilibrium A123CuFe4 phase is isostructural with A16Mn. The microstructure of this alloy has been examined after rapid solidification to ascertain the nature a
and morphology of the quasicrystalline and crystalline phases. The quasicrystalline phase was found to be of the decagonal type whereas the crystalline phase was Al13Fe4.
A large number of alloys have been made having a composition close to the stoichiometry Al65Cu20Fe15 in order to obtain on alloy completely free from crystalline phases. It was observed that an alloy of composition Al62.5Cu22.5Fe15., Fe,, in the cast and annealed condition is completely quasicrystalline.
Publications:
1 Structural Investigations on Some Rapidly Solidified Potential Quasi-crystal Forming Alloys, G.K. Dey, R.T. Savalia and S. Banerjee, Metallic and Semiconducting Glasses, edited by A.K. Bhatnagar. Key Engineering Materials Trans. Tech. Publications, Switzerland, 2987, Vol. 1, p.241-244
2 Endothermic Quasicrystalline-to-Crystalline Phase Transition in A16CuMg4, M.K. Sanyal, V.C. Sahni and G.K. Dey, Pramana Journal of Physics 28 (1987) L709 L712.
3. Evidence for Endothermic Quasicrystalline-Crystalline Phase Transitions in A16CuMg4, M.K. Sanyal, V.C. Sahni, G.K. Dey and L. Varshney, Nature, 328 (1987) 704-706
4. Phase Transitions in Quasicrystalline A4CuMg4, M.K. Sanyal, V.C. Sahni, G.K. Dey and L. Varshney, Physical Review, B 36, 1987, 2443-2445.
5. High Pressure Studies on Mg-Cu-Al and Mg-Zn-Al Alloys, C. Kamunakaran, S.N. Vaidya, G.K. Dey and D.K. Joshi and P. Ramachandra Rao, In Proceedings of DAE Symposium on Solid State Physics, BARC, Bombay, Dec. 27-31, 1987, Vol. 30C p. 104106.
6. Structural Relaxation in Al6CuMg4 Quasicrystals, M.K. Sanyal, VC. Sahni, L. Varshney, G.K. Dey and S. Banerjee, In Proceedings of DAE Symposium on Solid State Physics BARC, Bombay, December 27-31, 1987 V. 30C p. 114 - 115.
7. Crystallization and Structural Relaxation in Quasicrystalline Al6CuMg4, M.K. Sanyal, V.C. Sahni, G.K. Dey and S. Banerjee Int. Conf. on Modulated Structures, Polytypes and Quasicrystals, B.H.U., Varanasi, 1988. Proceedings Published in Phase Transitions page 35-37.
8. High Pressure Studies on Mg4CuAl6, Mg3Zr2Al2, Amorphous Ni(P) and Microcrystalline Pd(P), C. Kaninakaran, S.N. Vaidya, M.K. Totiani, S.N. Athavale and G.K. Dey, Inb A.K. Singh (ed) Proc. XIII AIRAPT Int. Conf on High Pressure Science and Technology, Bangalore 1991, Oxford and IBM Publishing Co., New Delhi, 316-318.
9. A Near Icosahedral Quasiperiodic Phase in Rapidly Solidified Mg32Al49, U.D. Kulkami, G.K. Dey, R.T. Savalia and S. Banerjee, Phil. Mag Let. 64 (1991) 169-174
10. Microstructural Studies on Rapidly Solidified Mg32(AlxZn1-x)49 - Potentially Quasi-crystal Forming Alloys, R. Banerjee, R.T. Savalia, E.G. Baburaj, G.K. Dey and U.D. Kulkarni, Mat. Sci. and Eng.. A165 (1993) 149 156.
11. Formation of Quasicrystalline phases in Rapidly Solidified Al23CuFe4, G.K. Dey, Deepak Prakash, R.T. Savalia, R.K. Mandal and S. Banerjee, Communicated to Scripts Metallurgic et Materialia (in press).
12. Formation of Metastable Phases in Rapidly Solidified M932(AlxZn1 x)49 Alloys, R. Banerjee, R.T. Savalia, N. Prabhu, D. Prakash, U.D. Kulkarni and G.K. Dey; Communicated to Scripts Metallurgica et Materialia.---------------------------------
THERMOCHEMICAL PROCESSING IN IRON REFRACTORY METAL
(V, Nb AND TI)-INTERSTITIAL (C, N) SYSTEMS
S. Adhikari and G.K. Dey
Metallurgy Division
The formation of refractory metal carbides and nitrides in both FCC and BCC iron based alloys plays a major role in controlling the microstructure and the mechanical properties of large variety of steels. The development of high strength low alloy steels (HSLA) and the surface hardenable steels are all based on the phenomena associated with the precipitation of refractory metal carbides and nitrides. The sequence, the mechanism and the kinetics of these precipitation processes are being covered in this study.
An experimental programme is underway in which iron based binary alloys containing refractory metals V, Nb and very low interstitial are being heat-treated in NH3/H2 and CH4/H2 environments to produce carbide and nitride precipitates in-situ. Ion nitriding is also being employed for the introduction of nitrogen in these alloys. The early stages of the formation and the subsequent growth these precipitates are being studied using TEM. In nitrided samples of Fe-V alloys the early stages are characterised by the mottled appearance of the matrix and the streaked diffraction patterns. The overall process is being modeled as concomitant operation of two processes namely clustering of substitutional solutes (V) and interstitial ordering within the solute rich regions. A remarkable similarity between the zone formation and this process is noted. In later stages various nitrides such as Fe16N2, Fe4N and VN have been found to appear. Their distinctive morphologies are being rationalised in terms of their registry with the matrix.
Publication
1. Nitride Precipitation in Iron-Vanadium-Nitrogen Alloy; S. Adhikari, G.K. Dey, S. Banerjee and V. Gopinathan; ICPM-1994.------------------------------
PRECIPITATION OF INTERMETALLIC PHASES IN INCONEL 718
M. Sundararaman, P. Mukhopadhyay and S. Banerjee
Metallurgy Division
The precipitation of intermetallic phases- the metastable y" (DO22 structure) and y' (LI 2 structure) phases and the equilibrium 8 (DOa, structure) phase in the commercial nickel base superalloy Inconel 718 has been investigated in the temperature range of 923 K - 1223 K. Spherical y' and ellipsoidal y" particles have been found to evolve through homogeneous nucleation. The precipitation of the former does not appear to precede that of the latter in this alloy. In a certain temperature range (973K - 1023K) a physical association between precipitates of the two types occurs frequently, leading to the development of a composite morphology. The development of this morphology is attributed to the operation of two mechanisms, namely, heterogeneous nucleation of y" on y' or y' on y" as well as the encounter between y' and y" or between y" particles during their growth or coarsening. Evidences for both types of mechanisms have been found in this work. Investigations on the coarsening kinetics of y' and y" particles have revealed that the particle size depends linearly on the cube root of ageing time. The coarsening rate of y' particles showing physical association with particles appears to be a little faster than that of unassociated y' particles.
The mode of nucleation of 8 phase at different temperatures has been investigated. At low temperatures, the 8 phase nucleates predominantly at grain boundaries and twin boundaries in a heterogeneous manner. At intermediate temperatures, nucleation occurs intragranularly as well as intragranularly. Nucleation within grains has been noticed to be associated with the geometric stacking faults which form within y" particles during their growth. On the basis of a comparison of the stacking sequence on the close packed layers in these structures, it has been concluded that the stacking faults within the particles correspond to the 8 phase stacking sequence. At higher temperatures 5 phase nucleates directly from the supersaturated solid solution. Some features of the precipitation of intermetallic phases in this alloy has been explained on the basis of the free electron concentration model. The effect of various alloying elements in altering the e/a ratio and, thereby, the relative stability of these, has been examined.
Publications
1. Some aspects of precipitation of metastable intermetallic phases in Inconel 718; M. Sundararaman, P. Mukhopadhyay and S. Banerjee; Metallurgical Transactions, Vol. 23A (1992) 2015.
2. Precipitation of the 8 -Ni3 Nb phase in two nickel base alloys; M. Sundararaman, P. Mukhopadhyay and S. Banerjee; Metallurgical Transactions, Vol. 19A (1988) 453.
3. Overlapping of y" variants in Inconel 718, M. Sundararaman and P. Mukhopadhyay; Materials Characterisation, 31 (1993) 191-196.---------------------
MICROSTRUCTURE AND PHASE STABILITY OF GAMMA-BASED TITANIUM ALUMINIDES
R.V. Ramanujan
Metallurgy Division
Two phase gamma-based titanium aluminides are attractive candidate materials in a number of high temperature land and aerospace applications. Titanium aluminides have recently successfully passed the demanding jet engine tests. These high strength, low density materials also have excellent creep and oxidation resistance and can replace traditional superalloys in applications, such as power generation, which requires high service temperatures for maximum efficiency. This activity has focused on the microstructure and phase stability of binary and ternary titanium aluminides (R.V. Ramanujan, Acta metall. mater., in press) and the following three
projects are underway:
The effect of silicon and boron on the phase transformations in TI-AI-X alloys. When the kinetics of the gamma to alpha + gamma phase transformation in binary Ti-Al alloys is compared to that of silicon-and boron-containing alloys it is found that the addition of silicon and boron can have a drastic effect on the thermodynamics and kinetics of the phase transformation. This transformation and the reverse alpha to gamma transformation form the basis for microstructural design of these alloys. It is interesting to note that while silicon slows down the kinetics and reduces the driving force for the gamma to alpha + gamma transformation, boron can completely suppress the transformation. A point which remains to be clarified is the mechanism by which silicon decreases the growth of the alpha laths in the gamma matrix at the same time increasing the density of precipitates relative to the binary alloy. Experiments are underway to test the theory that silicon acts by (I) reducing the stacking fault energy thus increasing the precipitate density and (2) reduces the ledge nucleation density by "poisoning" of the interface and reducing the growth rate.
Characterization of gamma/gamma twin and gamma/alpha interfaces
Modification of the gamma/gamma twin and gamma/alpha interfaces offers a potent method of increasing the toughness of gamma-based titanium aluminides. Modeling and experimental investigation of fcc:hcp interfaces has been undertaken in the past (R.V. Ramanujan et al, Acta Metall., vol. 40, 1992, pages 3421-3432 and pages 3433-3442) and the gamma/alpha-2 interface is one example of such an interface. Computation of the equilibrium concentration profile of the gamma/alpha 2, interface, the equilibrium dislocation structure and calculation of the chemical and structural components of the interfacial energy is being performed. The interfaces produced in Ti-48Al heat treated at 1350C for one hour followed by water quenching show well formed dislocation networks. However, the interfacial structure obtained by lath martensite formation in Ti-48AI-2Mn--2Nb alloys has not yet been studied. These interfaces can be further altered by thermomechanical treatment and this already promising microstructure can be further "improved" to yield better mechanical properties. Efforts are underway to examine the gamma/gamma twin and gamma/alpha-2 interfaces obtained in martensitic phase transformations in Ti-48AI-2Mn-2Nb alloys.
Phase diagram, stacking fault energies and APB energy calculations of the gamma + alpha-2, gamma + beta and gamma + B2 structures in Ti-AI-X alloys
Ternary additions to Ti-Al alter the relative phase stability of the (alpha 2, gamma, beta, and B2 phases. A systematic study, combining theoretical modeling with experimental measurements, of the effect of ternary additions on the relative phase stability of these phases has not been performed. It has been shown by Li, Ramanujan and Loretto (Y.G.Li, R.V. Ramanujan and M.H. Loretto, Proc. Intl. Conf. on Proc. and Props. of Materials, eds. M.H. Loretto and C.J. Beavers, MCE Pubins., U.K. (1992)) that the addition of 2 at% molybdenum to Ti-48AI alloys can result in the formation of gamma + B2 structure. However much larger amounts of chromium must be added to stabilize the gamma + B2 structure. The interest in studying the stability of the B2 and 0 phases is that the gamma + alpha and gamma + B2 structures are expected to have better mechanical properties compared to the gamma + alpha-2 structures. Phase diagram modelling combined with experimental results would be an useful guide to select new alloy compositions of TiAl based alloys. Experimentally, it has also been observed that the addition of Mo promotes the formation of planar defects such as twins, stacking faults and APBs while Cr promotes the formation of line defects and their dissociation. Quantitative estimates of the reason for this important observation which has an immediate bearing on the mechanical properties are not available and calculations are being performed to understand this phenomenon.-------------------------------
INVESTIGATION OF THE Ni3Al-Ni3V, Ni3AL-Ni3Nb AND Ni3V-Ni3Nb SYSTEMS
P. Mukhopadhyay, R.V. Ramanuian, J.B. Singh, M. Sundararamall
Metallurgy Division
"Mixed" intermetallic systems in which the desired properties of each of the intermetallics is combined is an attractive route for the preparation of novel structural intermetallics. Many intermetallics consist of ordered versions of the fcc and hcp phases. One example is that of gamma-based titanium aluminides which consists of alternating lamellae of the L10 (g)TiAl phase and the DO19(a) Ti3Al phase. The two phases reinforce each other and the mechanical properties of the two phase structure is superior to either one individually. Three other such systems are the Ni3Al-Ni3V, Ni3AL-Ni3Nb and Ni3V-Ni3Nb (DOa) pseudobinary systems. These systems exhibit some interesting features:
1. Phase transformations between the Ni3Al (LI2,gamma') phase, g (fcc) phase and the Ni3V (DO22,q) phase and similar phase transformations in the Ni3Al-Ni3Nb system can be conveniently studied.
2. In the Ni3Al-Ni3V system, the p-d interaction between the electrons of the Al and Ni atoms, often linked to the low ductility of intermetallics, is replaced through progressive additions of V (or Nb) by d-d interactions. This effect on the mechanical properties can be investigated. 3. Since V and Nb are in the same group in the periodic table (VB), the simultaneous study of the Ni3Al-Ni3V system and the Ni3AI-Ni3Nb system enables us to study the effect of the size of the atom and distinguish the size effect from the "chemical" effect mentioned above. 4. On the basis of free electron concentration model, replacement of V with Nb or Ta in Ni3V is not expected to bring about a change in crystal structure from DO,, to DO.. However, experimental observations are contrary to this prediction. It is worthwhile to investigate this transformation.
The experimental study of these systems, using optical microscopy, EPMA, TEM and mechanical testing was initiated by arc-melting buttons of the following compositions:
Ni3AI, 0.9Ni3Al-0.1V, 0.75Ni3Al-0.25V, 0.5Ni3Al-0.5V, 0.25Ni3Al-0.75V, Ni3V &;0.9Ni3Al-0.1Nb, 0.75Ni3Al-0.25Nb, 0.5Ni3Al-0.5Nb, 0.25Ni3Al 0.75Nb and Ni3Nb. Specimens from these buttons were heat treated at 1200C for three hours. A summary of the results of optical microscopy of as-cast and heat treated specimens are tabulated (Table 1).
Table 1: Microstructure of Ni3Al-Ni3V and Ni3Al-Ni3Nb alloys
COMPOSITION AS-CAST MICROSTRUCTURE HEAT TREATED STRUCTURE
Ni3Al dendritic mottled
0.9Ni3Al-0.1V cellular with ppts. cellular with coarsened
ppts. at cell boundaries
0.75Ni3Al-0.25V dendrites with ppts. coarsened dendrites
0.5Ni3Al-0.5V dendritic with ppts. large equiaxed grains
rod-shaped pots forming a
"bamboo" structure
0.25Ni3Al-0.75V similar to 0.5Ni3Al-0.5V coarsened dendrites
with fine scale
precipitation
Ni3V cellular ordered Ni3V forming
mosaic structure
0.9Ni3Al-0.1Nb dendritic coarsened dendritic
structure with pption.
in interdendritic
region
0.75Ni3Al-0.25Nb similar to 0.9Ni3Al-0.1Nb similar to 0.9Ni3Al-0.1Nb
0.5Ni3Al-0.5Nb highly cored dendritic similar to as-cast
structure
0.25Ni3Al-0.75Nb rod shaped ppts forming similar to as-cast
a bamboo structure
structure
Ni3Nb similar to coarsened columnar
0.25Ni3Al-0.75Nb grains; absence of ppts.
with coring between
the rod shaped ppts.
The stability of the "bamboo" microstructure at 1200C for the 0.25Ni3Al 0.75Nb composition suggests that this alloy can be investigated as a possible "in-situ" composite. The following alloys, which are useful in studying phase transformations between the fcc and hcp based phases have been heat treated and prepared for detailed TEM examination: 0.5Ni3Al-0.5V, 0.25Ni3Al-0.75V, 0.5Ni3Al-0.5Nb.
In the Ni3V-Ni3Nb systems, an alloy having the composition Ni3(O.75V 0.25Nb), on ageing below the critical temperature for ordering, transforms to a mixture of phases with the DO22 and DO. structures. The concentration of niobium in the DO22 structure has been determined by chemical analysis to be only 4 at%.
Mechanical testing of these alloys has been initiated.---------------------------
JOINING CERAMICS
S.N. Athavale, N.C. Soni, M.R. Gonal, Ram Prasad and M.K. Totlani
Metallurgy Divsion
Many of the potential advanced applications for structural ceramics (such as heat engines or heat exchangers) are very critically dependent on the technology for reliably joining ceramic components to form complex assemblies, unit lengths of ceramic material to form large systems or ceramic components to metals. Ceramic-to-metal feed through's have potential use in a variety of applications including ultra high vacuum (UHV). Extensive studies on the ceramic alumina-to-metal joining have led to the optimisation of producing reliable alumina-to-metal seals having a helium leak rate of 10-9 cc/sec.
The studies are being extended to other ceramic materials and also the development of active brazing materials.
Papers Published
1. Direct Bonding of Metals to Ceramics : Copper and Nickel to Sintered Alumina by S.N. Athavale, P.B. Shrivastva and M.K. Totlani, Proc. of BRNS Symposium on 'Sintering and Sintered Products', BARC, Bombay (1979), p 677.
2. Ceramic-Metal Joining by M.K. Totlani, S.N. Athavale, N.C. Soni, Ram Prasad and C.K. Gupta, Bull. Ind. Vac. Soc., vol. 23, No. 3 (1992), 21.------------------------
DEVELOPMENT OF HIGH TEMPERATURE OXIDE SUPERCONDUCTORS
Ram Prasad, N.C. Soni, K. Adhikary, A. Guinar and M.R. Gonal
Metallurgy Division
Metallurgy Division over the past five years has vigorously pursued a comprehensive eon development of high temperature oxide superconductors. During this period, various synthesis routes have been developed for YBa2CU3O7, YBa2CU4O8, Bi-2212, Bi-2223 and Pb-Sr-R-Ca Cu-O. These include solid state methods employing ambient and reduced pressures as well as wet chemical routes. The effect of oxygen content on the structure and superconducting properties of YBaCuO and RE BaCuO (RE = rare earth's) has also been studied. Magnetic properties and structure of quenched and slow cooled compounds were investigated which proved the coexistence of superconductivity and strong paramagnetism in these compounds. This was the first group to report the synthesis of Pb2Sr2 RCu2Ox superconducting compounds without calcium addition. Extensive experimentation on the effect of different kinds of ionic substitutions (magnetic and non-magnetic) at various lattice sites in YBaCuO, RBaCuO and BiSrCaCuO compounds on the structure and properties has been carried out to understand the nature of superconductivity in high To oxides.
Another important area of investigation has been the different fabrication routes for high T oxides. Sintering behaviour of these oxides was studied in detail and bulk densities upto 96% c
T.D. were achieved in cold compaction and sintering process by modification of initial powder characteristics. This was one of the earliest groups to demonstrate the importance of oxidesilver composites in the fabrication process. It was proved that the silver addition resulted in a marked improvement in fabricability and critical current density, without any detrimental effect on the transition temperature. Experiments were also conducted on shock wave compaction of pure and composite compositions. Effect of microstructural characteristics on the superconductivity has also been studied through optical and electron microscopy with a view to improve the critical current density. Grain aligned structures were obtained using deformation, fugitive liquid and partial melting techniques. The effort on structure-property correlation in high Tc oxides is continued.
Publications
1 Composites of superconducting YBa2Cu307-y with silver; Ram Prasad, N.C. Soni, Ashok Mohan, S.K. Khera, K.U. Nair, C.K. Gupta, C.V. Tomy and S.K. Malik; Materials Letters 7(1,2), 9 (1988).
2 Consolidation of Y-Ba-Cu-0 powders by shock-loading; N.C. Soni, Ram Prasad, Ashok Mohan, M.D. Vora, S. Banerjee, C.V. Tomy, S.K. Malik, H.S. Yadav and K.R.K. Rao; Pramana J. of Physics 32 (6), 801 (1989).
3 Superconducting and magnetic studies on GdBa2(Cu1-x Fex)3 O7+z oxide system; S.K. Malik, C.V. Tomy, D.T. Adroja, S.K. Dhar, R. Nagarajan, Ram Prasad and N.C. Soni, Solid State Comm. 67, 521 (1988)
4 Superconductivity in 70K range in Ca-free Pb-Sr-R-Cu-0 oxide system", Ram Prasad, N.C. Soni, K. Adhikary, S.K. Malik and C.V. Tomy, Solid State Comm. 76(5), 667 (i 990).
5 Magnetic susceptibility Resistivity and 151 Eu Mossbauer studies on Zn-substituted EuBa2Cu307-y", C.V. Tomy, R. Nagarajan, S.K. Malik, Ram Prasad, N.C. Soni and K. Adhikary, Solid State Comm. 75(1), 59 (1990).
6 Magnetic susceptibility and beat capacity measurements on Prerich PrBa2-xPrx Cu3O7-y compounds, S.K. Malik, S.M. Pattalwar, C.V. Tomy, Ram Prasad, N.C. Soni and K. Adhikary, Physical Review B, 46, 524 (1992).
7. Arya, G.P. Das, H.G. Salunke an S. Banerjee, J. Phys.: Cond.. Matt. (1994), in press.
END