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Development of Sustainable Cold Spray Coatings and 3D Additive Manufacturing Components for Repair/Manufacturing Applications: a Critical Review

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Development of Sustainable Cold Spray Coatings and 3D Additive Manufacturing Components for Repair/Manufacturing Applications: a Critical Review coatings Review Development of Sustainable Cold Spray Coatings and 3D Additive Manufacturing Components for Repair/Manufacturing Applications: A Critical Review Sunil Pathak 1 and Gobinda C. Saha 2,* ID 1 Faculty of Engineering Technology, University Malaysia Pahang, Pahang 26300, Malaysia; [email protected] 2 Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada * Correspondence: [email protected]; Tel.: +1-506-458-7784 Received: 30 June 2017; Accepted: 10 August 2017; Published: 14 August 2017 Abstract: This review article presents the findings of a comprehensive state-of-the-art literature review of the scientific and technological progress of the cold spray process in the field of repair/remanufacturing using the concept of additive manufacturing. A thorough study was conducted on the potential of this technology to form (a) both thin and thick coatings; (b) the ability to fabricate 3D freeform components in a single process, while benefiting from reduced residual stress level compared to conventional thermal spray coatings processes such as high velocity oxy-fuel (HVOF) or plasma spraying. A systematic overview of the process technology, particularly focusing on the suitability of ceramic-metallic (cermet) composite particles used as feedstock in the deposition was conducted; further elaboration was made pertinent to particle impact and bonding mechanisms during the deposition. Keywords: cold spray; HVOF; coatings; additive manufacturing; remanufacturing 1. Introduction Thermal spray technologies have evolved from being “tough to regulate” to “controlled” processes since their first industrial applications in the early 1980s. Initially, the hard tool industry was the focus of thermal spray based coatings development. The process is generally described by methods in which coating is formed from melted or semi-melted droplets, with a starting material in the form of powder, wire or rod and is fed into a flame produced by a spray gun [1]. Depending on the nature of the energy source (kinetic and/or thermal) the deposited material can provide unique characteristics of the coatings or 3D additive manufacturing components. In particular, the coatings are used right across the spectrum of engineering industries most notably in the repair and manufacturing of components to enhance their surface properties, at the option of low-cost, lightweight, and sustainable investment. There are many examples of evolvement especially HVOF (high velocity oxy-fuel) and plasma spraying for producing coatings with low porosity and high adhesion [2]. These advanced coatings are used to give a predictable extension of in-service lifetime or to provide properties superior to untreated substrates for a more efficient performance in a particular application [3–10]. Advanced coatings are required to impart many characteristics to components; a few of the applications worth mentioning are wear resistance, corrosion resistance, heat resistance, oxidation resistance, electrical resistance, electrical conductance, fatigue strength, clearance control, self-healing, self-cleaning, non-stick, water repellent, anti-microbial, bio-compatible, bio-active, diffusion barrier, and high absorption capability [11–13]. These are often enabling disruptive technologies in a diverse range of products such as gas turbine engines, upstream pumps, drill bits, architectural glass, orthopedic implants, etc. Coatings 2017, 7, 122; doi:10.3390/coatings7080122 www.mdpi.com/journal/coatings Coatings 2017, 7, 122 2 of 27 Coatings 2017, 7, 122 2 of 27 TheThe energyenergy sourcesource inin thermalthermal sprayspray coatingcoating developmentdevelopment is usedused toto heatheat thethe feedstockfeedstock toto aa moltenmolten oror semi-moltensemi‐molten state.state. The resultant heated particles are acceleratedaccelerated andand propelledpropelled towardtoward aa preparedprepared substratesubstrate byby eithereither processprocess gasesgases oror atomizationatomization jets.jets. UponUpon impactimpact aa bondbond isis formedformed withwith thethe surface,surface, withwith subsequentsubsequent particles causing thickness build-upbuild‐up and forming a lamellar structure. TheThe propertiesproperties ofof thethe depositdeposit maymay dependdepend uponupon itsits density,density, thethe cohesioncohesion betweenbetween thethe depositeddeposited particles,particles, andand particleparticle adhesionadhesion toto thethe substratesubstrate surface.surface. For many materials, however, thethe useuse ofof highhigh processprocess temperaturetemperature causescauses coatingscoatings toto bebe internally-fracturedinternally‐fractured duedue toto decarburization,decarburization, dissolution, andand delaminationdelamination atat leastleast [[14].14]. For oxygen-sensitiveoxygen‐sensitive materials for instance it is often requiredrequired toto produceproduce coatingscoatings inin anan expensiveexpensive vacuumvacuum chamber,chamber, thusthus limitinglimiting broaderbroader penetrationpenetration ofof thermalthermal sprayspray intointo many many commercial commercial applications applications [15 –[15–18].18]. Traditional Traditional thermal thermal spray spray processes processes are often are found often inadequatefound inadequate to use for to temperature-sensitive use for temperature‐ materialssensitive andmaterials applications and applications where coatings where are coatings required are for repair/manufacturingrequired for repair/manufacturing with thickness with of a few thickness millimeters. of a Thesefew millimeters. limitations wereThese overcome limitations by awere new memberovercome of by the a thermalnew member spray of family, the thermal namely spray the cold family, gas dynamicnamely the spray. cold gas dynamic spray. ColdCold sprayspray isis anan emergingemerging process,process, discovereddiscovered fromfrom aa theoreticaltheoretical andand experimentalexperimental observationobservation relatedrelated to a supersonic two two-phase‐phase flow flow (gas (gas + + solid solid particles) particles) experimentation experimentation in in a wind a wind tunnel tunnel in in1990 1990 [19]. [19 ].It Itoriginated originated in inthe the former former Soviet Soviet Union Union by by a a group group of of researchers researchers at the InstituteInstitute ofof TheoreticalTheoretical and and Applied Applied Mechanics Mechanics (ITAM) (ITAM) of the of Siberian the Siberian Branch Branch of the Russianof the Russian Academy Academy of Sciences, of whoSciences, correlated who correlated the interaction the interaction of a two phase of a two flow phase with flow the surface with the of surface an immersed of an immersed body (particle) body and(particle) demonstrated and demonstrated that it was that possible it was to possible obtain coatingsto obtain from coatings solid from particles solid at particles room stagnation at room temperaturestagnation temperature of the flow. of Until the thatflow. time, Until it wasthat commonlytime, it was accepted commonly that accepted particles that needed particles to be needed heated toto be high heated temperatures to high temperatures ensuring their ensuring melting their in melting the gas in flow the togas obtain flow to a obtain coating, a coating, and that and it wasthat impossibleit was impossible to obtain to obtain a coating a coating by spraying by spraying particles particles in the in solid the solid state. state. Since Since then, then, the technology the technology has enjoyedhas enjoyed few few iterations iterations and and by far by thefar biggestthe biggest success success has has been been largely largely embodied embodied by theby the spraying spraying of metallic/metalof metallic/metal alloy alloy particles particles with with the helpthe help of high of high velocity velocity particle particle impingement impingement [20]. Later [20]. onLater many on patentsmany patents were filed were and filed granted and using granted this using process this and process for the developmentand for the development of the spray equipment of the spray for depositionequipment of for variety deposition of materials of variety such of asmaterials metals, such alloys, as mixtures, metals, alloys, and polymers mixtures, [ 21and]. polymers [21]. ThereThere isis aa veryvery basicbasic differencedifference betweenbetween conventionalconventional thermalthermal sprayspray techniquestechniques andand thethe coldcold sprayspray process.process. Thermal spray techniques require both thermal and kinetickinetic energiesenergies forfor thethe coatingcoating formation,formation, whilewhile coldcold sprayspray usesuses onlyonly kinetickinetic energy,energy, as as depicted depicted in in Figure Figure1 .1. Figure 1.1. Sources of energy inin aa conventionalconventional thermalthermal sprayspray vs.vs. coldcold gasgas dynamicdynamic sprayspray process.process. In cold spray there is no melting of particles taking place as the process temperature stays below In cold spray there is no melting of particles taking place as the process temperature stays below 800 °C, while in HVOF this can go up to 3000 °C. Softer materials (easier to plastically deform) and 800 ◦C, while in HVOF this can go up to 3000 ◦C. Softer materials (easier to plastically deform) and materials that have smaller heat capacities (easier to achieve shear instability) have so far benefited materials that have smaller heat capacities (easier to achieve shear instability) have so far benefited from the use of this technology. This distinctive feature enables it to be used
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