X-ray residual stress measurements on cold-drawn steel wire

The interplanar spacing d{hkl} versus sin2 ψ distributions were measured for the 211, 310, 220 and 200 reflections from severely cold-drawn 0.7% C steel wire with a diameter of 0.25 mm. From the shape of the curves it was concluded that, as well as a 110 fibre texture and elastic anisotropy, plastic anisotropy of the ferrite crystals may be an important cause of the non-linearity in d{hkl} versus sin2 ψ. The shape of the curves, and therefore the residual state of stress of the wire, is influenced by the drawing parameters, i.e. the drawing die cone angle and the number of stages

Texture development and transformation strain of a cold-rolled Ti50-Ni45-Cu5 alloy

Shape memory alloys (SMAs) are finding increased use as functional materials in the aerospace, energy and medical industries 1 J. van Humbeeck, Shape Memory Materials and Phenomena—Fundamental Aspects and Applications, p. 3771, vol. 246, MRS, Pittsburgh, PA (1992).(1), (2) and (3). Shape memory behaviour is based on the recovery of large amounts of induced strain upon heating and/or unloading. This transformation strain is a result of the reversible growth of certain favoured martensite variants during martensite transformation and/or stressing [4] and [5]. For single crystal SMAs, the favoured variants are those which result in the maximum transformation strain for a specific orientation. This has been well established for several common single crystal SMAs such as TiNi, CuZnAl and CuAlNi [4] and [6].\ud \ud For polycrystalline SMAs, it is not clear which variants are favoured. Anisotropic behaviour in SMAs has been interpreted based on the anisotropy data of single crystal materials using the concept of the selection of favoured martensite variants. This has met with only limited success in work on NiTi alloys due to the lack of information about which variants are formed [7] and [8]. An investigation of the anisotropic behaviour of textured SMAs was thus conducted in order to determine which martensite variants develop during thermal cycling of a commercial TiNiCu SMA. The relationship between the observed variant development, changes in texture and anisotropic shape memory behaviour are discussed in light of models using the concept of favoured martensite variants

FIM-ATOM PROBE STUDY OF THE PRECIPITATION IN A Ti46.3. Ni53.7 ALLOY

The precipitation process in a B2-TiNi-alloy has been studied during aging between 873-973 K for various aging times. Earlier reported results obtained with TEM/EDX-analyses showed the development of three different precipitates. The compositions, based on crystallographic calculations were found to be between 55-65 at % Ni. In the present study FIM/AP-analyses have been used to verify these compositional variations. At the early stages of precipitation only Ti3Ni4 is formed which could be analysed both by EDX as well as FIM/AP-analysis. The results of AP-analysis seem to be in better agreement with the calculated value of 57.1 at % Ni than the EDX results. The FIM images of the alloys show no crystallographic poles which is ascribed to the heavily twinned martensite transformation of the ordered B2-phase during cooling in the FIM. The Ti3Ni4-phase could be identified in the FIM images by the brightness and clear pole formation. The Ti2Ni3- and the Ti5Ni9-phase showed very brittle behaviour in the FIM, and AP-analyses showed better agreement with the calculated values than EDX, but can not be treated as conclusive yet

The texture development of It-Ni-Cu wire during thermomechanical cycling

An investigation has been carried out on the texture of Ti-44Ni-5Cu (at %) shape memory alloy wire. The texture of the B2 and monoclinic phases has been determined as a function of the degree of cold deformation during the drawing process and the number of cycles on thermomechanical cycling. After cold drawing and anlealing (823 K, 180 s) under tensile stress, the [110], [1(-1)0] [101] and [(-1)01] directions in the monoclinic phase are parallel to the wire axis. In this condition a preference for the [(-1)01] component is observed. On heating the wire above Af and cooling down, this preference disappears. Subsequently the preference develops again on thermomechanical cycling. The B2 phase shows in all conditions a fiber texture. The observed preference of the [(-1)01] fiber texture component in the monoclinic phase is discussed in terms of strain accomodation during plastic deformation