Microstructure of interpass rolled wire + arc additive manufacturing Ti-6Al-4V components

Mechanical property anisotropy is one of the issues that are limiting the industrial adoption of additive manufacturing (AM) Ti-6Al-4V components. To improve the deposits’ microstructure, the effect of high-pressure interpass rolling was evaluated, and a flat and a profiled roller were compared. The microstructure was changed from large columnar prior beta grains that traversed the component to equiaxed grains that were between 56 and 139 μm in size. The repetitive variation in Widmanstätten alpha lamellae size was retained; however, with rolling, the overall size was reduced. A “fundamental study” was used to gain insight into the microstructural changes that occurred due to the combination of deformation and deposition. High-pressure interpass rolling can overcome many of the shortcomings of AM, potentially aiding industrial implementation of the process.EPSRC, AirBu

Investigation of low current gas tungsten arc welding using split anode calorimetry

Most previous split anode calorimetry research has applied high weld currents which exhibit pseudo Gaussian distributions of arc current and power density. In this paper we investigate low current arcs and show that both the current and power distributions have minima in the centre – varying significantly from the expected Gaussian profile. This was postulated due to the formation of the arc with the copper anode and the tungsten cathode. Furthermore, a number of parameters were varied including the step size between measurements, anode thickness and anode surface condition as well as cathode type and tip geometry. The step size between measurements significantly influenced the distribution profile and the anode thickness needed to be above 7 mm to obtain consistent results

Cultural Resources Survey of the Leander Rehabilitation Center, Williamson County, Texas

In August-September 1996, personnel from Prewitt and Associates, Inc., conducted a cultural resources survey of ca. 725 acres of the former Leander Rehabilitation Center. The project area lies adjacent to U.S. Highway 183 and FM 620 in southern Williamson County, Texas. The survey resulted in additional documentation of one previously recorded prehistoric archeological site (41 WM452), the identification and recording of four historic archeological sites (41WM892, 41WM893, 41WM896, and 41WM897), and reconnaissance-level documentation of 45 historic buildings and structures. Site 41WM452 is an extensive upland lithic scatter and lithic procurement site which lacks subsurface deposits, features, and datable materials. Site 41WM892 is a wood-chopper camp that contains a number of rock alignments and limited artifact deposits dating to the first decade of the twentieth century. Site 41WM893 is a remnant of a railroad spur used during the 1937-1941 construction of Marshall Ford Dam (now Mansfield Dam). Site 41WM896 contains a small number of features and sparse artifact deposits associated with the 1937-1945 Rhodes farmstead. Site 41WM897 is an isolated historic well with unknown associations. None of these archeological sites contains important information, and it is recommended that they be considered not eligible for listing in the National Register of Historic Places or for designation as State Archeological Landmarks. The 45 buildings and structures, at 36 locations, are associated with the former State Dairy and Hog Farm. This farm was established in 1942, expanded after 1945, and reached its peak years of production as a hog farm between 1950 and the late 1960s, Created to serve the needs of the State Board of Control and the State Hospital, the facility is significant for its success in food production for eleemosynary institutions in Austin and throughout Texas, as well as for its role in the application of modern psychiatric treatment based on the therapeutic value of manual labor. Among the surveyed resources are dwellings, an office and warehouse building, a dormitory, a variety of agricultural buildings and structures, and infrastructural elements, all built between 1943 and 1955. Twenty-one of the 45 surveyed resources are recommended as being eligible for listing in the National Register of Historic Places under Criteria A and C as Contributing resources in a historic district and for designation as State Archeological Landmarks

Effectiveness and Acceptance of Mobile Learning

Mobile Learning (M-Learning) is no longer a novelty. Thousands of post-secondary education institutions and millions of workforce and distance-education students worldwide consider M-Learning a mainstream, pervasive, learning delivery mode. It is a different and alternate approach to Face-to-Face, Distance Learning (D-Learning), and Electronic Learning (E-Learning). A gap exists in the literature regarding the effectiveness of M-Learning. It is important to evaluate this learning delivery mode against Face-to-Face learning. This study examines M-Learning effectiveness vis-à-vis Face-to-Face and investigates the extent to which students accept the delivery of learning conducted through this new paradigm. A quasiexperimental research design is proposed to determine the impact of M-Learning on student performance and to uncover factors that influence user acceptance of M-Learning

The effectiveness of combining rolling deformation with wire-arc additive manufacture on β-Grain refinement and texture modification in Ti-6Al-4V

In Additive Manufacture (AM), with the widely used titanium alloy Ti–6Al–4V, the solidification conditions typically result in undesirable, coarse-columnar, primary β grain structures. This can result in a strong texture and mechanical anisotropy in AM components. Here, we have investigated the efficacy of a new approach to promote β grain refinement in Wire–Arc Additive Manufacture (WAAM) of large scale parts, which combines a rolling step sequentially with layer deposition. It has been found that when applied in-process, to each added layer, only a surprisingly low level of deformation is required to greatly reduce the β grain size. From EBSD analysis of the rolling strain distribution in each layer and reconstruction of the prior β grain structure, it has been demonstrated that the normally coarse centimetre scale columnar β grain structure could be refined down to < 100 μm. Moreover, in the process both the β and α phase textures were substantially weakened to close to random. It is postulated that the deformation step causes new β orientations to develop, through local heterogeneities in the deformation structure, which act as nuclei during the α → β transformation that occurs as each layer is re-heated by the subsequent deposition pass

Improved microstructure and increased mechanical properties of additive manufacture produced TI-6AL-4V by interpass cold rolling

Distortion, residual stress and mechanical property anisotropy are current challenges in additive manufacturing (AM) of Ti-6Al-4V. High-pressure, interpass rolling was applied to linear AM parts and resulted in a change from large columnar prior β grains to a completely equiaxed microstructure with grains as small as 89 μm. Moreover, α laths thickness was also reduced to 0:62 μm. The change in material microstructure resulted in a substantial improvement of all mechanical properties tested, which were also totally isotropic. In rolled specimens, maximum measured strength and elongation were 1078MPa and 14% respectively, both superior to the wrought material. Distortion was reduced to less than half. Rolling proved to be a relatively easy method to overcome some of the critical issues which keep AM from full industrial implementation

Arc instabilities during split anode calorimetry with the TIG welding process

Split anode calorimetry investigations of tungsten inert gas (TIG) arcs were conducted using a large-diameter shielding gas nozzle. Some conditions displayed arc symmetry whilst others proved distinctly asymmetric. The variation of welding current and electrode tip to workpiece distance (ETWD) was studied. Decreasing the ETWD was found to increase the current density towards the arc axis but similar to a previous study of the authors, Gaussian distributions were not observed. The gas nozzle was designed to produce laminar gas flow and sound shielding behaviour; however, anode surface oxidation was found after welding, presumably caused by shielding gas contaminated with oxygen through the welding sequence. Therefore, axial arc symmetry was influenced by random effects. The conditions and reasons for the observed phenomena are explored within this paper