On the decomposition of β phase in some rapidly quenched titanium-eutectoid alloys

Microstructural evolution and interfacial reactions during active metal vacuum brazing of Ti (grade-2) and stainless steel (SS 304L) using a Ag-based alloy containing Cu, Ti, and Al was investigated. A Ni-depleted solid solution layer and a discontinuous layer of (Ni,Fe) 2 TiAl intermetallic compound formed on the SS surface and adjacent to the SS-braze alloy interface, respectively. Three parallel contiguous layers of intermetallic compounds, CuTi, AgTi, and (Ag,Cu)Ti 2 , formed at the Ti-braze alloy interface. The diffusion path for the reaction at this interface was established. Transmission electron microscopy revealed formation of nanocrystals of Ag-Cu alloy of size ranging between 20 and 30 nm in the unreacted braze alloy layer. The interdiffusion zone of b-Ti(Ag,Cu) solid solution, formed on the Ti side of the joint, showed eutectoid decomposition to lamellar colonies of a-Ti and internally twinned (Cu,Ag)Ti 2 intermetallic phase, with an orientation relationship between the two. Bend tests indicated that the failure in the joints occurred by formation and propagation of the crack mostly along the Tibraze alloy interface, through the (Ag,Cu)Ti 2 phase layer.

Section: Titanium-braze Alloy Interfacesupporting

confidence: 73%

Section: Titanium-braze Alloy Interfacementioning

confidence: 99%

Microstructure and Interfacial Reactions During Active Metal Brazing of Stainless Steel to Titanium

Laik

Shirzadi

Tewari

et al. 2013

“…As for the near-eutectoid alloys, the decomposition mode appeared to be predominantly a pearlitic transformation. [26,27] Thus, in the present study, with the evidence of the decomposition of b phase, it can be deduced that a eutectoid point is highly likely to exist at the composition around Ti-9.1 pct Ni-2.81Cr-2.19Co-2.17Al-1.54V for the multicomponent system.…”

Section: B Decomposition Of B-timentioning

confidence: 79%

“…In fact, previous work on the solid-state eutectoid decomposition of a number of Ti-X alloys [25,26,27] showed that there were two different modes of eutectoid decomposition of b phase: the nonlamella (bainite) mode and the lamellar (pearlite) mode. Bainite phase has been defined as a nonlamellar, noncooperative, competitive product of the transformation, while pearlite has been defined as a lamellar, cooperative product of the eutectoid decomposition.…”

Section: B Decomposition Of B-timentioning

confidence: 96%

Solidification Behavior and the Evolution of Phase in Laser Rapid Forming of Graded Ti6Al4V-Rene88DT Alloy

Lin

Yue

Yang

et al. 2007

The graded material of Ti6Al4V-Rene88DT superalloy, which has shown the potential to be applied in aeroengines, was fabricated from prealloyed metal powders using the technique of laser rapid forming (LRF). A compositional gradient, from 100 pct Ti6Al4V to Ti6Al4V-38 pct Rene88DT, was achieved within a thickness of laser deposit of 54 mm. The solidification behavior and the phase evolution of the compositionally graded material were studied. The results of the X-ray diffraction (XRD) analysis together with the metallographic study showed that a series of phase evolutions, a + b fi a + b + Ti 2 Ni fi b + Ti 2 Ni, along the compositional gradient have occurred. The hardness value of the graded material was measured along the compositional gradient, and the results were explained in terms of the various phases present. The condition for columnar-to-equiaxed transition observed in the graded material was explained, based on Hunt's criterion. Finally, the morphology of b + Ti 2 Ni anomalous eutectic is discussed.

“…Also, it is known that even during rapid quenching, the b-phase undergoes eutectoid decomposition in near-eutectoid Ti-Cu alloys. [30,31] Therefore, during the process of cooling from the brazing temperature, the b-Ti(Cu) solid solution that formed in the region 8, underwent active eutectoid transformation to the product phases a-Ti and CuTi 2 in the form of lamellar aggregates of phase mixture.…”

Section: Braze Alloy-titanium Interfacementioning

confidence: 99%

Microstructure and Interfacial Reactions During Vacuum Brazing of Stainless Steel to Titanium Using Ag-28 pct Cu Alloy

Laik

Shirzadi

Sharma

et al. 2014

Microstructural evolution and interfacial reactions during vacuum brazing of grade-2 Ti and 304L-type stainless steel (SS) using eutectic alloy Ag-28 wt pct Cu were investigated. A thin Ni-depleted zone of a-Fe(Cr, Ni) solid solution formed on the SS-side of the braze zone (BZ). Cu from the braze alloy, in combination with the dissolved Fe and Ti from the base materials, formed a layer of ternary compound s 2 , adjacent to Ti in the BZ. In addition, four binary intermetallic compounds, Cu 3 Ti 2 , Cu 4 Ti 3 , CuTi and CuTi 2 formed as parallel contiguous layers in the BZ. The unreacted Ag solidified as islands within the layers of Cu 3 Ti 2 and Cu 4 Ti 3 . Formation of an amorphous phase at certain locations in the BZ could be revealed. The b-Ti(Cu) layer, formed due to diffusion of Cu into Ti-based material, transformed to an a-Ti + CuTi 2 eutectoid with lamellar morphology. Tensile test showed that the brazed joints had strength of 112 MPa and failed at the BZ. The possible sequence of events that led to the final microstructure and the mode of failure of these joints were delineated.