Effects of Annealing on the Fabrication of Al-TiAl3 Nanocomposites Before and After Accumulative Roll Bonding and Evaluation of Strengthening Mechanisms (original) (raw)
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Journal of Alloys and Compounds, 2018
A novel method to fabricate aluminum metal-matrix composites reinforced by mono-dispersed TiAl 3 intermetallic particles, by cold-roll bonding, heat treatment, followed by accumulative roll bonding (ARB), is demonstrated. Roll bonding of 1100-Al sheets inserted with Ti powder was carried out at room temperature with 50% thickness reduction. Complete conversion of the initial Ti particles into TiAl 3 intermetallic was achieved by a post-rolling annealing treatment at 590 C for 2 h, which results in the formation of coarse TiAl 3 particles along the interface of the original 1100-Al sheets. Subsequent ARB process was applied to break up and disperse the TiAl 3 phase, and after 5 cycles of ARB, an aluminummatrix composite with mono-dispersed TiAl 3 particles of submicron sizes was achieved. The Al matrix also undergoes dynamic recrystallization during the ARB process to result in a fine-grained microstructure (size less than 500 nm). The hardness, tensile strength and elongation of the Al/TiAl 3 composite were found to increase with the number of ARB cycles. The tensile strength of the Al/TiAl 3 composite after the 5th cycle reaches 400 MPa, which is significantly higher than the 300 MPa of monolithic 1100-Al processed in the same way. The tensile elongation of the Al/TiAl 3 composite after 5 cycles of ARB exhibits a good value of~8%, with a ductile fracture mode. This is the first successful attempt to achieve Al-matrix nanocomposites reinforced by mono-dispersed TiAl 3 intermetallic based on an ARB method.
Diffusion bonding of TiAl using reactive Ni/Al nanolayers and Ti and Ni foils
Materials Chemistry and Physics, 2011
The diffusion bonding of TiAl using reactive Ni/Al multilayer thin films with Ti and Ni foils was investigated. Bonding experiments were performed at 800 and 900 • C, at a pressure of 5 MPa and for bonding times of 30 and 60 min. The bonding surfaces were modified by sputtering, by deposition of Ni and Al nanolayers to increase the diffusivity at the interface, and Ti and Ni foils were used to fill the bond gap. The microstructure and chemical composition of the interfaces were investigated by scanning electron microscopy, electron backscattered diffraction and by energy dispersive X-ray spectroscopy. Sound joints were obtained with a combination of reactive multilayer thin films and Ti and Ni thin foils. Several AlNiTi intermetallic compounds were formed in the interface region. The mechanical properties of the joints were evaluated by nanoindentation and shear strength tests. Using foils in-between the nanocrystalline multilayers, which would be a useful method for correcting the absence of flatness of the parts to be joined, has drawbacks as it induces the formation of hard, brittle intermetallic compounds, responsible for the low shear strength of the joints.
Intermetallics, 2005
A new family of Al-matrix composites containing g-TiAl intermetallic reinforcement particles has been processed by extruding aluminium and TiAl powders in different proportions up to 50% of the intermetallic. To modify the size and distribution of the intermetallic powders they were used in three different states, namely, atomised, and milled for 1 and 5 h. The yield strengths of the composites are very dependent on the volume fraction of the reinforcement and follow a Hall-Petch type relationship on the interparticle spacing. Much of the strength of the composites is retained up to temperatures of 250 8C, with an activation energy responsible for the deformation process measured as QZ96G5 kJ/mol for all materials, indicating that the high temperature deformation is controlled by diffusion along dislocations in the aluminium matrix. The plastic ductility is also dependent on the volume fraction of particles but is not much affected by the particle state. The composites containing 25% particles have higher ductilities, ranging between 9 and 12% at all temperatures and for all particle states. q
Diffusion bonding of gamma-TiAl using modified Ti/Al nanolayers
Solid state diffusion bonding has been successfully employed to join -TiAl alloys. Processed in vacuum, at high temperature and pressure, the thin interfaces and the lack of structural discontinuity across the interface are the main advantage of this joining technique. An interlayer made of alternated Ti and Al nanometric layers that increases the diffusivity at the joint interface, was used in order to assist the bonding process of -TiAl alloys. The use of Ti/Al interlayer has efficiently reduced the joining temperature. Sound joints have been achieved at a temperature of 900 ◦C under a pressure of 50 MPa in vacuum. In the present work Cu was added as third element to the Ti/Al multilayers and its effect improved the bonding quality. The interface microstructure was studied by scanning and transmission electron microscopy.
Role of intensive milling in mechano-thermal processing of TiAl/Al2O3 nano-composite
Advanced Powder Technology, 2012
In this research a nano-composite structure containing of an intermetallic matrix with dispersed Al 2 O 3 particles was obtained via mechanical activation of TiO 2 and Al powder mixture and subsequent sintering. The mixture has been milled for different lengths of time and then as a subsequent process it has been sintered. Phase evolutions in the course of milling and subsequent sintering of the milled powder mixture were investigated. Samples were characterized by XRD, SEM, DTA and TEM techniques.