In the present work, nanocrystalline FeAl and FeAl-Al2O 3 composite were synthesized by high energy ball milling and subsequent compaction by spark plasma sintering. Microstructural changes during all stages of processing are studied using X-ray analysis. After 20 h of milling, the disordered FeAl and some amount of Fe rich solid solution was obtained in both of these compositions. Subsequent heat treatment results in formation of ordered FeAl. However, disordering of FeAl was observed in both compositions after spark plasma sintering. Nanocrystallinity is retained in both the compositions even after sintering at high temperature of 1,000 C. Very high hardness of ~575 HV1 and ~600 HV1 was exhibited by FeAl and FeAl-Al2O3 composite. © 2013 Indian Institute of Metals.

Budaraju Srinivasa Murty

Department of Metallurgical and Materials Engineering

Ravi Sankar Kottada

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Transactions of the Indian Institute of Metals

The B2-Aluminide matrix (FeAl and NiAl) with in-situ Al2O3 reinforcement were synthesized using reactive milling. The oxides (Fe2O3 and NiO) were reduced by Al during high energy milling to form Al2O3. The 20 h ball milled powders were consolidated using spark plasma sintering (SPS). To understand the densification mechanisms during SPS, sintering was performed at various temperatures (750–850 °C) and applied pressures (25–100 MPa). The creep parameters are evaluated from the densification data obtained during SPS using the model proposed by Bernard and Granger. In addition, independent constant-stress compression creep studies were conducted on the dense SPS pellets. The creep studies were performed on the composites at 800 °C at different stresses (100–500 MPa). The densification studies and compression creep studies are correlated based on the creep parameters obtained from both these studies and corroborated by TEM studies of the crept samples. This correlation is found to be valid even for the in-situ composites. Thus, the analysis of densification data can be helpful in predicting the creep behavior and useful for designing the new creep resistant alloys or composites. © 2017 Elsevier B.V.

Journal of Alloys and Compounds

Verification of correlation between densification during spark plasma sintering and compressive creep of ultrafine-grained in-situ Al2O3-reinforced B2 aluminide matrix composites

In modern fast-breeder nuclear power plants, on-site fusion welding of austenitic stainless steel AISI 304L and commercially pure titanium pipes is called for. The application imposes stringent requirements on these joints in terms of tensile strength, bend ductility, and corrosion resistance in boiling nitric acid. However, fusion welding of stainless steel to titanium directly is a near impossibility because of inevitable brittle intermetallic formation between iron and titanium and, consequently, serious weld cracking problem. All things considered, the best way to realize these joints is to make use of solid-state welded stainless steel/titanium (SS/Ti) dissimilar pipe joining inserts or adaptors. Towards this end, many solid-state welding techniques such as diffusion bonding, friction welding, and explosive welding have been tried in past, but without much success. In the current study, solid-state welding of SS rods to Ti rods was attempted in spark plasma sintering equipment. The potential of this new process, termed spark plasma welding, for dissimilar metal welding are discussed. © 2015, The Indian Institute of Metals - IIM.

Spark Plasma Welding of Austenitic Stainless Steel AISI 304L to Commercially Pure Titanium

NiAl-30 vol.% Al2O3 nanocomposite has been synthesized from the NiO-Al-Ni powder mixture by carrying out reactive milling in toluene medium and subsequent heating. The NiO reduction and the ordered NiAl phase formation occur simultaneously during milling. The unreacted NiO present in as milled powder is reduced by Al/NiAl at 420 °C on heating. Subsequent heating leads to the formation of a small amount of Ni3Al phase before it transforms completely to NiAl phase above 900 °C. Amorphous alumina is formed as the product of NiO reduction and it transforms to stable α-Al2O3 at 1000 °C via the formation of metastable transition γ-Al2O3. After heating to 1120 °C, the 20 h milled powder consists of nanocrystalline NiAl phase and α-Al2O3 with a crystallite size of 115 ± 40 nm size and 11 ± 3 nm, respectively. © 2009 Elsevier Ltd. All rights reserved.

Intermetallics

Synthesis of in-situ NiAl-Al2O3 nanocomposite by reactive milling and subsequent heat treatment

The effect of mechanical activation on NiO-Al reaction has been investigated by carrying out high energy ball milling using toluene as the process controlling agent. NiO reduction reaction progresses gradually and a maximum of 70% reduction has been observed in 20 h of milling. Amorphous alumina forms as the product of NiO reduction and it transforms to stable α-Al2O3 at 1000 °C via the formation of metastable transition γ-Al2O3. The activation energy of NiO reduction in unmilled powder is 277 kJ/mol whereas in 20 h milled powder the activation energy has been reduced to 150 kJ/mol. © 2010 Elsevier B.V. All rights reserved.

Mechanical activation of aluminothermic reduction of NiO by high energy ball milling

Scripta Materialia

A new mechanism for field-assisted processing and flash sintering of materials

In contrast to the widely reported beneficial aspects of spark plasma sintering in developing materials with better properties, we report here two interesting aspects recorded with difficult-to-sinter titanium diboride: (a) in situ formation of second phase (TiB) and (b) inferior hardness (by ∼30%) and elastic modulus (by ∼20%) for spark plasma sintered TiB2, with respect to hot pressed TiB2. The formation of TiB is discussed with reference to the enhanced reaction kinetics in the presence of pulsed electric field. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Journal	Transactions of the Indian Institute of Metals
ISSN	09722815
Open Access	No