Joseph William Newkirk

Applications of a hybrid manufacturing process for fabrication of metallic structures

Purpose – This paper sets out to summarize the current research, development, and integration of a hybrid process to produce high‐temperature metallic materials. It seeks to present the issues and solutions, including the understanding of the direct laser deposition process, and automated process planning.Design/methodology/approach – Research in simulation and modeling, process development, integration, and actual part building for hybrid processing are discussed.Findings – Coupling additive and subtractive processes into a single workstation, the integrated process, or hybrid process, can produce metal parts with machining accuracy and surface finish. Therefore, the hybrid process is potentially a very competitive process to fabricate metallic structures.Originality/value – Rapid prototyping technology has been of interest to various industries that are looking for a process to produce/build a part directly from a CAD model in a short time. Among them, the direct laser deposition process is one of the f...

Abrasive wear properties of Cr-Cr3Si composites

Abstract A series of composites based on the Cr–Cr 3 Si system, and containing between 50 and 100%Cr 3 Si, were fabricated by hot pressing. These composites have high stiffness, good thermal conductivity, excellent chemical resistance, and high temperature creep and oxidation resistance, making them potential candidates for hard-facing applications and cutting tools in harsh environments. In this study, the Cr–Cr 3 Si composites were abrasion tested at ambient temperatures in order to evaluate their wear properties. Single scratch tests were performed to give insight into material removal mechanisms. Although like most metal silicides, these materials behave in a brittle manner, the results of this study indicate that the addition of a ductile second phase (Cr) can enhance both their fracture toughness and abrasive wear resistance. The addition of 10% of the rare earth oxide Er 2 O 3 improves the density of the composite, but has no apparent influence on the wear resistance.

Powder characterisation techniques and effects of powder characteristics on part properties in powder-bed fusion processes

ABSTRACT Powder-bed fusion is a class of Additive Manufacturing (AM) processes that bond successive layers of powder to facilitate the creation of parts with complex geometries. As AM technology transitions from the fabrication of prototypes to end-use parts, the understanding of the powder properties needed to reliably produce parts of acceptable quality becomes critical. Consequently, this has led to the use of powder characterisation techniques such as scanning electron microscopy, laser light diffraction, X-ray photoelectron spectroscopy, and differential thermal analysis to study the effect of powder characteristics on part properties. Utilisation of these powder characterisation methods to study particle morphology, chemistry, and microstructure has resulted in significant strides being made towards the optimisation of powder properties. This paper reviews methods commonly used in characterising AM powders, and the effects of powder characteristics on the part properties in powder-bed fusion processes.

Influence of details of reactor history on microstructural development during neutron irradiation

Abstract Microstructurally-oriented irradiation experiments are shown in this paper to be strongly dependent on details of reactor history that frequently are not brought to the experimenters attention. In some cases, these details can dominate the experiment so as to produce very misleading results. To aid in the design and interpretation of microstructurally-oriented experiments, a number of studies are reviewed to highlight history effects and then guidelines are presented to minimize the impact of reactor history in new experiments.

The Jominy end quench for light-weight alloy development

The Jominy end quench test is well known as a method of measuring hardenability in steels. In nonferrous alloys, there is a desire to determine the effect of quenching on final properties after heat treating. The Jominy end quench test offers a method for studying many quenching conditions with a minimum of samples. The potential for developing a new understanding of the complex response of nonferrous alloys to processing conditions, especially quenching, will be presented. Examples of the properties measured on Jominy end quench specimens of aluminum and titanium alloys will be presented.

Evaluation of methods to produce tough Cr3Si based composites

Abstract Several methods of improving the toughness of Cr–Cr 3 Si composites produced by powder metallurgy have been examined. Mechanical alloying of Cr-3.92 w/o with 0.5 w/o V showed the best improvement in toughness of this phase. Replacing Cr 3 Si with a (Cr 0.57 , Mo 0.43 ) 3 Si, produced in situ from a mechanically alloyed powder, offered a slight improvement in toughness. By combining these phases a composite was produced with a toughness greater than 10 MPa m −2 . Other second phase materials were also examined for providing second phase toughening of Cr 3 Si. These include an Fe–Al alloy, Ni 3 Al+B, and 304L stainless steel. At the level of 25 v/o these materials at present do not appear to offer much improvement in toughness. Cr–Cr 3 Si composites were hot forged to produce a more layered microstructure and refine the microstructure of arc-melted samples. The layered microstructure should be tougher, but has not been tested yet.

Influence of cold-work and phosphorus content on neutron-induced swelling of ternary Fe-Cr-Ni alloys

Abstract Phosphorus additions can either increase or decrease void swelling of simple ternary Fe-Cr-Ni alloys during neutron irradiation, depending on the irradiation temperature, phosphorus level and cold-work level. Phosphorus is shown in these simple alloys to exert its primary influence while in solution. Phosphide precipitation appears to play only a secondary role in void swelling. The role of cold-work is not always to suppress swelling in Fe-Cr-Ni and Fe-Cr-Ni-P alloys, however, particularly at relatively higher irradiation temperatures, where cold-working often increases swelling substantially. Coldworking also appears to alter somewhat and suppress formation of phosphide precipitates.

Direct laser deposition of Ti-6Al-4V from elemental powder blends

Purpose This paper aims to achieve Ti-6Al-4V from Ti, Al and V elemental powder blends using direct laser deposition (DLD) and to understand the effects of laser transverse speed and laser power on the initial fabrication of deposit’s microstructure and Vickers hardness. Design/methodology/approach Two sets of powder blends with different weight percentage ratio for three elemental powder were used during DLD process. Five experiments with different processing parameters were performed to evaluate how microstructure and Vickers hardness change with laser power and laser transverse speed. Energy dispersive X-ray spectroscopy, optical microscopy and Vickers hardness test were used to analyze deposits’ properties. Findings This paper reveals that significant variance of elemental powder’s size and density would cause lack of weight percentage of certain elements in final part and using multiple coaxial powder nozzles design would be a solution. Also, higher laser power or slower laser transverse speed tend to benefit the formation of finer microstructures and increase Vickers hardness. Originality/value This paper demonstrates a new method to fabricate Ti-6Al-4V and gives out a possible weight percentage ratio 87:7:6 for Ti:Al:V at powder blends during DLD process. The relationship between microstructure and Vickers hardness with laser power and laser transverse speed would provide valuable reference for people working on tailoring material properties using elemental powder method.

Vision-based defect detection in laser metal deposition process

Purpose – Laser metal deposition (LMD) is a type of additive manufacturing process in which the laser is used to create a melt pool on a substrate to which metal powder is added. The powder is melted within the melt pool and solidified to form a deposited track. These deposited tracks may contain porosities or cracks which affect the functionality of the part. When these defects go undetected, they may cause failure of the part or below par performance in their applications. An on demand vision system is required to detect defects in the track as and when they are formed. This is especially crucial in LMD applications as the part being repaired is typically expensive. Using a defect detection system, it is possible to complete the LMD process in one run, thus minimizing cost. The purpose of this paper is to summarize the research on a low-cost vision system to study the deposition process and detect any thermal abnormalities which might signify the presence of a defect. Design/methodology/approach – Durin...

Microstructure and physical properties of iron carbide films formed by plasma enhanced chemical vapor deposition

Abstract We report the structure and properties of iron-containing films deposited on glass substrates maintained at temperatures between 200 and 500 °C. The films investigated were Fe 3 O 4 , Fe 7 C 3 , Fe 3 C 1 and α-Fe, deposited at substrate temperatures of 200, 300, 400 and 500 °C, respectively. The measured SEM grain sizes from these 200–700 nm thick films were in the 50–350 nm range. X-ray diffraction and scanning electron microscopy show larger grains and increased crystallinity in the films deposited at higher substrate temperatures. The larger grain sizes and increased crystallinity are consequences of bulk diffusion and surface recrystallization. The sheet conductivities of the films increase with increasing film deposition temperature, due to coarser grain structures and higher iron to carbon ratios in the higher temperature films. The phases remain unchanged after annealing at 400 °C for 4 h. X-ray diffraction and scanning electron microscopy show evidence of bulk rearrangement and a reduction of thickness in the annealed films.