Processing behavior of nanocrystalline NiAl during milling, sintering and mechanical loading and interpretation of its intergranular fracture Mohammad Bagher Rahaei a,b,c,⇑ , Dechang Jia b a Nanomaterials and Nanotechnologies Department, Tomsk Polytechnic University (TPU), Tomsk 634050, Russia b Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology (HIT), Harbin 150080, China c Standard Research Institute, Alborz / Karaj 31745-139, Iran article info Article history: Received 14 May 2014 Received in revised form 8 October 2014 Accepted 21 October 2014 Available online 29 October 2014 Keywords: Nanocrystalline NiAl Sintering Mechanical properties Microstructure Dislocation Intergranular fracture abstract Processing behavior of Ni and Al powders during milling, sintering and compression loading was evaluated using SEM, TEM and XRD-Rietveld’s refinement analysis techniques. Nanocrystalline NiAl intermetallic along with microstrain and dislocations on its micro- structure was obtained after milling. Sintering of nanocrystalline powders at 1180 °C under a pressure of 48 MPa for 1 h time by hot press technique resulted in grain growths toward ultrafine along with decreasing of microstrain and dislocations on microstructure. Obtaining a microstructure of ultrafine grained NiAl resulted in improvement of mechan- ical properties. Intergranular fracture was characterized by the coupling of dislocations at grain boundaries that caused to formation of voids/cracks with progressive loading. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The aluminide systems have shown good performance in high-temperature, oxidation and corrosion conditions. Among aluminides, NiAl has a high interest due to its favorable property/cost ratio. NiAl phase has a significantly higher melting temperature than the constituent metals Ni and Al indicating a much strong bonding between the unlike Ni and Al atoms. Compared to other metallic materials, the processing of aluminides is rendered somewhat more challenging due to their very high melting points [1,2]. Several techniques for production of NiAl powders have been reported using elemental powders of Ni and Al such as self- propagating high temperature synthesis (SHS) [3] and mechanical alloying (MA) [4]. Among these, MA offers a number of advantages for processing intermetallic compounds such as grain refinement that improve mechanical properties [4,5].A variety of processes for achieve a strong, useful compact parts by sintering exist: including pressureless sintering, hot press- ing (HP), hot isostatic pressing, self propagating high-temperature synthesis, spark plasma sintering, etc. [6]. Hot pressing is a method that pressure and temperature are applied simultaneously. It has been established that the energy available for densification is increased by the application of pressure during sintering, providing several processing and property advan- tages such as reduction of densification time and temperature, inhibition of grain growth and minimization of residual porosity [6]. Recently, the potential use of materials in structural applications by significant hardening through grain size http://dx.doi.org/10.1016/j.engfracmech.2014.10.022 0013-7944/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +7 9528916449; fax: +86 451 86414291. E-mail address: m.b.rahaei@gmail.com (M.B. Rahaei). Engineering Fracture Mechanics 132 (2014) 136–146 Contents lists available at ScienceDirect Engineering Fracture Mechanics journal homepage: www.elsevier.com/locate/engfracmech