A novel method for metal–diamond composite coating deposition with cold spray and formation mechanism

This paper describes the application of cold spray to the deposition of a diamond grade pre-coated with Cu and Ni. This is the first time that pre-coated diamond powders are used as the sole feedstock without the addition of binders (ductile phases) in cold spraying. The experimental results showed that it was possible to manufacture thick metal–diamond composite coatings onto an Al alloy substrate with high diamond fraction in the coating and without phase change. Results from this paper also have demonstrated a new methodology for the deposition of metal–diamond/ceramic composite coating with the cold spray technique

International Thermal Spray Conference (ITSC)

Diamond reinforced copper matrix composites (DCMC) has great potentials for heat sinks applications due to their excellent thermal properties. Cold Spray, as a relatively emerging coating technique, is able to fabricate coatings or bulk materials at entire solidstate, significantly lowering the risk of oxidation, phase transformation and high thermal residual stress because of the low pr ocessing temperature. In this paper, thick DCMC coatings were fabricated via cold spray using copperclad diamond powder or its mixture with pure copper powder. It was found that cold spray due to its low processing temperature was able to avoid the graphitization of diamond in the DCMC coatings. Using the pure clad diamond powder only , the diamond in the original feedstock was almost completely retained in the coating which contained more than 40 wt.% diamond. Such high mass fraction of diamond has never been achieved in previous cold spray works using premixed powders. The mechanically mixed powder of clad diamond and copper also exhibited great retainbility for diamond; the diamond fraction in the coating was even larger than that in the original feedstock. Besides, the most important finding here is the additional copper powders acted as a buffer, effectively preventing the fracture of diamond in the coating

Observations of Surface Acoustic Wave Strain and Resistive Strain Measurements on Broaching Tools for Process Monitoring

The monitoring of high end material removal processes continues to develop to greater levels of technical sophistication which in turn enable greater levels of insight into the process phenomena occurring at the tool-chip interface. The broaching process is a traditional machining process which is used extensively in the manufacture of some of the most expensive components of the aero engine. As a relatively slow cutting process with low degrees of freedom, broaching could be a target for strain based monitoring. It is well known that strain gauges provide a rich source of data when installed close to the cutting process. This research provides insight into the resistive strain gauge measurements during broaching. The paper also specifically focuses on the use of surface acoustic wave based strain measurement and provides some initial observations on the strain data available during tooth loading and cutting scenarios in broachin

9th CIRP Conference on Intelligent Computation in Manufacturing Engineering

Biomedical grade polymers are commonly used in applications where surface finish and dimensional accuracy are key, such as in t otal joint replacement and intraocular lenses, yet relatively little research has been conducted into the machining of these materials. It has been established that workpiece temperature has a lar ge effect on machinability in soft polymers , with alterations to the chip formation mechanism p ossible when workpiece temperature is adequately controlled. This is due to the change in material behaviour at the glass tran sition temperature, which varies with the composition and crystallinity of the polymer. In polymers which have low glass transition te mperatures, liquid nitrogen cooling is used, in some cases with a control system used to regulate the workpiece temperature during machinin g. This work concentrates on the machining of Ultra High Molecular Weig ht Polyethylene (UHMWPE) workpieces which have been pre - cooled before mach ining. Past work has concentrated on the development of a measurement chain for the monitoring of polymer machining, and characterising the machining of UHMWPE at ambient temperature, wh ile varying tool and process parameters. Little work has been done on the cryogenic machining of UHMWPE, though it is known that the hi gh crystallinity of UHMWPE alters thermomechanical behaviour w hen compared to conventional blends of polyethylene, and the glass transition temperature is in the region of - 120?C. The aim of this work is to p rovide insight into the effect of workpiece temper ature on machinability and surface quality in UHMWPE

ITSC 2018?Proceedings of the International Thermal Spray Conference

This research demonstrates the use of cold spray (CS) as an additive manufacturing process to manufacture reflective aluminium coatings. Nitrogen was used as a carrier gas at various gas heating temperatures. Following deposition, the coatings were finished using a number of machining and/or polishing processes to surface roughness values of 20-150 nm. The samples were characterised with respect to total reflectivity within the wavelength range of 400-1800 nm, porosity, surface roughness, and density. The reflectivity of the coatings approached that of bulk material, and 99% dense coatings were obtained. Increasing the gas heating temperature did not decrease the porosity with the lowest gas heating temperature found to deliver the best reflectivity. This work demonstrates that CS can be used to coat thin layers of aluminium onto various materials, which can be subsequently polished to create composite reflectors. This provides a novel reflector with the reflectivity of aluminium, and the structural and thermal properties of the substrate material, allowing for greater flexibility in the manufacture of reflectors

ITSC 2019 - Proceedings of the International Thermal Spray Conference

Cold spray (CS) is an additive manufacturing process which has recently gained interest within research and select high-end production systems; however, one of the primary factors limiting the deployment of this process is the relatively poor mechanical properties of the coatings in the as-sprayed state as compared with bulk counterparts. Therefore, this paper details the mechanical performance of Al 6061 CS coatings heat treated using a novel focused IR device. The heat treatment of the coatings was performed in-process with the aim of improving the ductility and strength of the CSed coatings processed using nitrogen carrier gas. The mechanical properties of the heat treated samples were compared to a traditional annealing process and an as-sprayed sample by tensile testing dog bone samples. It was found that the rapid IR heat treatment process delivered advantages with regard to mechanical properties when compared to the untreated state showing an increase in the UTS of the coatings by 52% and an increase in the elongation at failure by 43%. This work demonstrates that rapid heat treatment can be carried out on a CS coating, allowing targeted improvement of mechanical properties over load-bearing components in a more time-effective way than traditional heat treatment techniques allow

Texture and Microstructural Features at Different Length Scales in Inconel 718 Produced by Selective Laser Melting

Nickel-based Inconel 718 is a very good candidate for selective laser melting (SLM). During the SLM process, Inconel 718 develops a complex and heterogeneous microstructure. A deep understanding of the microstructural features of the as-built SLM material is essential for the design of a proper post-process heat treatment. In this study, the microstructure of as-built SLM Inconel 718 was investigated at different length scales using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electron backscatter diffraction (EBSD) was also used to analyze the grain morphology and crystallographic texture. Grains elongated in the build direction and crossing several deposited layers were observed. The grains are not constrained by the laser tracks or by the melt pools, which indicates epitaxial growth controls the solidification. Each grain is composed of fine columnar dendrites that develop along one of their <100> axes oriented in the direction of the local thermal gradient. Consequently, prominent <100> crystallographic texture was observed and the dendrites tend to grow to the build direction or with occasional change of 90° at the edge of the melt pools. At the dendrite length scale, the microsegregation of the alloying elements, interdendritic precipitates, and dislocations was also detected