Revealed as a process for surface functionalization and repair, cold spray is currently used as a reliable additive manufacturing process thanks to its ability to fabricate dense solid-state deposits with high deposition efficiency. However, cold-sprayed deposits generally present limited mechanical and structural properties due to manufacturing defects such as microporosities and weak interfacial particle bonding. As solutions, post-processing methods such as heat treatment or hot isostatic pressing are proposed to reduce manufacturing defects and optimize final deposit properties. This paper investigates the heat treatment effect on structural and mechanical features of cold sprayed 3D Aluminium part by comparing deposits properties evolution with the additive growth in the as sprayed and heat-treated states. Thus, a study is carried out to identify the right heat treatment conditions for optimizing deposits properties.

In this work, hot isostatic pressing (HIP) is used to reduce interior defects, adjust the microstructure, and improve the tensile properties of cold-sprayed Ti6Al4V. Optical microscope and X-ray tomography were used to characterize pore morphologies and porosity evolution. XCT reconstructions show that fully dense Ti6Al4V alloy with an equiaxed microstructure were achieved. Tensile testing shows that strength and ductility were improved as well because of enhanced diffusion and resultant metallurgical bonding.

The potential of additive manufacturing has reached a point where the techniques are considered highly relevant for production purposes. In general, the manufacturing industry greets the new approach with enthusiasm, as it offers innovative designs and potentially reduced production costs. However, questions arise concerning the durability of additively manufactured components. This paper describes industrial trials with laser cladding and precipitation hardening heat treatment of thin-walled structures with the 17-4 PH stainless steel alloy. Due to the great relevance of the AM production methods for the aviation industry, the mechanical strength of the alloy given by the MMPDS document is used as a baseline. In order to improve the properties of the produced specimens, hot isostatic pressing was applied. The results show that a post processing treatment consisting of a HIP cycle and a conventional precipitation hardening, vastly improves the mechanical strength and elongation values of printed specimens, causing them to exceed the specified values.

The standard technique for applying zirconium (Zr) to uranium (U) is roll bonding, where a thin foil of Zr is placed on each side of a U plate which is then encased in steel and rolled at high temperatures. This study evaluates an alternative approach in which Zr layers are plasma sprayed on U and then clad with aluminum (Al) by hot isostatic pressing. The interface region between the Zr and Al is examined by SEM, revealing a reaction layer consisting of Al, Zr, and Si. SEM images show good conformance between the Al sheet and Zr surface along with the presence of Al in the porous Zr. Initial test results indicate that increased interface roughness and Al penetration into the plasma-sprayed Zr have the potential to improve bond strength by impeding crack propagation in the reaction layer.

This study examines the influence of nano- and near-nano grains in bulk powder metal processing thus providing a baseline for understanding the potential of nanopowders for thermal spray application. Two light alloys (Al and Ti) and two tungsten carbide blends (WC-NiCrBSi and WC-CoCr) are cryomilled into nanocrystalline powders. The nanopowders are consolidated via hot isostatic pressing or spark plasma sintering and tested along with consolidated forms of virgin (micron scale) grains, shedding light on property improvements achieved through nanograined materials. HVOF coatings produced from nano- and micro-crystalline powders are tested as well, and the results are correlated with the improvements observed in the consolidated material forms.

Die-casting moulds are subjected to severe conditions of cyclical thermal and mechanical loads, as well as chemical and mechanical wear. Dies mostly fail due to a combination of wear mechanisms. Heat checking, erosion, melt corrosion and soldering often lead to complete die failure. Ceramic plasma-sprayed coatings have a great potential for die protection, since they are chemically inert, and show high form stability at elevated temperatures. Furthermore, they show good resistance against thermal shock due to the porous state of the coated layer and low Young’s modulus. In the present study, the influence of hot isostatic pressing on thermal fatigue resistance of plasma spraying coatings is investigated. Thermal and thermomechanical tests were applied to characterise their ability to protect dies. The coatings were evaluated by residual stress measurements, metallography, hardness test and X-ray diffraction.

The aim of this preliminary investigation was to ascertain the synergetic potential of two process technologies of thermally spraying and HIPing (Hot Isostatic Pressing) for tribological applications and address the key design factors, which need to be considered for successful applications of HIPed thermal spray WC-NiCrBSi coatings. The relative performance of the as-sprayed and hot isostatically pressed WC-NiCrBSi functionally graded coatings was investigated in sliding wear conditions. Results indicate that HIPing post-treatment can improve the sliding wear resistance of WC-NiCrBSi coatings. These coatings were deposited by a High Velocity Oxy-Fuel - JP5000 system and HIPing process was carried out at two different temperatures of 850°C and 1200°C. This study shows that un-capsulated HIPing can be successfully applied to functionally graded WC-NiCrBSi coatings, which has economical as well as technical incentives for industrial applications. Sliding wear tests were carried out using a high frequency reciprocating ball on plate rig using steel and ceramic balls. Results are discussed in terms of powder manufacture method, microstructural investigations, phase transformation, mechanical properties and residual stress investigations. Phase analysis by X-ray diffraction revealed transformations, which altered the phase composition such as the elimination of secondary phase W2C and metallic W and the formation of new phases containing Ni, Si and B after the post-treatment. The measurements of hardness, Young’s modulus and residual stress indicate that substantial improvements can be achieved due to simultaneous application of temperature and pressure during the HIPing post-treatment. Hardness and Young’s modulus measured by indentation method, increased after the HIPing process due to the transformations in the morphology and phase composition of the coatings. The residual stress evaluations by sin2Ψ technique using synchrotron x-ray diffraction showed a relaxation of residual stress fields in the coating with increasing temperature of the HIPing process.

Coatings obtained by thermal spray techniques are widely used in many industrial applications where wear and abrasion resistance is required. High Velocity Oxy-Fuel (HVOF) spraying represents the state of the art of such types of coatings. The high velocity of the particles achieved during the spraying process and relatively low temperatures at the point of application enhance bond strength and eliminates substrate deformation by thermal effects. These aspects make the process attractive for high value components. In this work the electrochemical behaviour of both as-sprayed and HIPed Stellite 6 coatings are compared. Hot Isostatic Pressing (HIPing) consists of simultaneous applications of high pressure and high temperature. In this paper HIPing has been used as a post-treatment process for HVOF coating. Electrochemical DC anodic polarisation corrosion experiments were conducted in seawater at 18°C, 30°C, 40°C, 50°C, 70°C and 90°C. To support the electrochemical tests, detailed microscopy was conducted after corrosion tests to determine the attack mechanisms.

The age-old problem of fixing a flaw in an airfoil of a vane or bucket that is otherwise serviceable, has been resolved by the careful blending of two known technologies, HVOF (High Velocity Oxy Fuel) and HIP (Hot Isostatic Pressing). This recently patented process facilitates the successful replacement of parent material as to allow a component which would otherwise be taken out of service to be reused in a “like new” condition. HVOF spraying of an airfoil employs the same material as the parent part. This process by itself will not provide sufficient adhesion to cause a complete marriage of materials. HIP’ing completes the union. Resulting “RECAST” repaired components display the same mechanical and physical properties as the parent material.

The aim of this experimental study was to comprehend the relative performance and failure modes of WC-NiCrBSi Thermal Spray coatings in As–Sprayed and HIPed (Hot Isostatically Pressed) conditions in rolling/sliding contact. Recently a number of scientific studies have addressed the fatigue performance and durability of Thermal spray coatings in rolling/sliding contact, but as of yet there have been no investigations on Thermal Spray Coatings which have undergone the post treatment HIPing. The understanding of the mechanisms of failure in rolling /sliding contact after HIPing is therefore critical in optimising the parameters associated with this post treatment to achieve superior performance. Coatings were deposited by a JP5000 system and HIPing was carried out at two different furnace temperatures of 1123K and 1473K. At both HIPing temperatures the rate of cooling was kept constant at 8°C/minute. Rolling Contact Fatigue tests were conducted using a modified four ball machine under various tribological conditions of contact stress, configuration and lubrication. Results are discussed in terms of as-sprayed and HIPed surface examination of rolling elements using Scanning Electron Microscope (SEM) and Light Microscope.

Hot isostatic pressing has been shown to be an effective post treatment for thermal spray coatings, improving hardness, density, and microstructure as well as metallurgical bonding between splats. In this study, the sliding wear resistance of as-sprayed and post-treated WC-Co deposited by HVOF is evaluated by means of ball-on-disk testing and the effects of HIPing are assessed based on SEM and XRD analysis, hardness measurements, and fracture toughness tests. Changes observed in the WC-Co layers, including the precipitation of carbides and the elimination of secondary phase W 2 C, are also discussed. Paper includes a German-language abstract.

ZrB 2 -SiC composites are considered a class of promising materials for aerospace applications such as nose and leading edges of re-entry vehicles. Results on such materials obtained by hot isostatic pressing have confirmed their high resistance to the oxidation at temperature up to 2000°C. Ongoing work has shown that such materials can be obtained in the form of coatings by means of Plasma Spraying techniques. On this regard, the most critical aspect was correlated to the decomposition of the SiC phase at a temperature quite lower than the melting point of ZrB 2 . Experimental evidence indicated that such decomposition can be avoided when a proper methodology of preparation of the starting powders is adopted, and if suitable thermal spraying parameters are selected. In any case, high temperature oxidation testing (up to 1800°C) confirmed the outstanding behaviour of this materials obtained by plasma spraying. This paper is focussed on preliminary studies of oxidation behaviour for plasma sprayed ZrB 2 -SiC composites suitable for thermal protection shields.

Pre-alloyed, plasma spheroidized powders were used as feedstock in the plasma spraying of functionally graded ZrO 2 /NiCrAlY coatings. The advantage of using pre-alloyed powders was to ensure chemical homogeneity and promote uniform density along the graded layers, and these pre-alloyed powders could be successfully used to prepare the different inter-layers of functionally graded coatings. The microstructure, density and microhardness changed gradiently in the ZrO 2 /NiCrAlY coatings. The bond strength of ZrO 2 /NiCrAlY coatings with different graded layers was measured. Results showed that for as-sprayed coatings with the same thickness, the bond strength increased with the number of graded layers. The bond strength of the coatings with five graded layers was about twice as high as that of the duplex coatings because of the significant reduction of the residual stress in the coatings. Experimental results also showed that the bond strength of as-sprayed coating increased significantly after hot isostatic press (HIP) and vacuum heat treatments, and the reason can be attributed to the densification of the microstructure, the decrease of defects in the coatings, inter-diffusion between layers and further reduction in the residual thermal stress.