Title: Tantalum Based High-Pressure Cold Spray Coatings on Stainless Steel Substrate

• The researchers of this study are "Jagannadh V.S.N. Sripada, Media F. Gallant, Gobinda C. Saha, and Reeti Singh, Jan Monday". It was published in the Key Engineering Materials Vol. 813, and has been available online since July 2019.
•  Tantalum (Ta) was chosen in the research as the feedstock coating to be deposited on AISI 1018 carbon steel substrate using the high-pressure cold spray (HPCS) method.
•  Tantalum's properties include good resistance to corrosion, good ductility, and notable hardness. It is also known for its high heat resistance, heat conductivity, and electrical conductivity.
• The cold spray coating technology allows the deposition of powder feedstock, such as Tantalum, without melting. As the feedstock powder is propelled through a nozzle using high velocities, they plastically deform upon impact, causing a good bond with the substrate.
• This study aimed to achieve a "dense and nonporous coating microstructure" with high efficiency in terms of deposition.
• As a result, the material created after coating the stainless steel substrate with Tantalum exhibited an ultimate tensile strength of 442 MPa and 77 MPa adhesion strength.

Title: Deposition behavior, microstructure and mechanical properties of an in-situ micro-forging assisted cold spray enabled additively manufactured Inconel 718 alloy

• The study was authored by Xiao-Tao Luo, Meng-Lin Yao, Ninshu Ma, Makoto Takahashi, and Chang-Jiu Li. It was published in Materials & Design Vol. 155 on October 2018.
• In the study, in-situ micro-forging (MF) was introduced to the cold spray technique by facile approach. The large 410 stainless steel (410SS) particles were mechanically mixed with IN718 powder so that it could be hammered and plastically deformed by the MF particles during the cold spray process. The cold spray with the in-situ micro-forging technique created a fully dense deposit.
• The created fully dense IN718 deposit was achieved without any form of contamination due to low impact velocity.
• The addition of 50 vol% of MF particles into the IN718 powder also decreased the porosity from 5.6% to 0.26%.
• An increased deposition efficiency was also observed for the first time as induced by oxide scale removal.
• The result shows that the ultimate strength of the material increased from 96 MPa to 464 MPa due to the micro-forging technique. Additional heat treatment at 1,200 degrees Celsius for 6 hours resulted in a higher strength of 1,089 MPa.

Title: Strategy of incorporating Ni-based braze alloy in cold sprayed Inconel 718 coating

• This research study was conducted by Wen Sun, Ayan Bhowmik, Adrian Wei YeeTan, Fei Xue, Iulian Marinescu, Feng Li, and Erjia Liu. Their study was published in Surface abd Coatings Technology, Vol. 358 on January 2019.
• A high-pressure cold spray process was performed to deposit Ni-based superalloy (Inconel 718) and Ni-based braze alloy (MAR-M 002) composite coatings on the Inconel 718 substrate.
• The researchers found that the Mar-M 002 particles were uniformly distributed within the composite coatings and was successfully embedded in the substrate via cold spraying.
•  Heat treatment after the cold spray deposition was also conducted as part of the strategy of incorporating the composite coatings.
• The heat treatment process also reduced the coating porosity as it enhances the chemical diffusion between Inconel 718 and MAR-M 002 particles.
• The results also showed the heat-treated material with composite coatings of Inconel 718 and MAR-M 002 had about 810 MPa tensile strength, which is 17% higher than the heat-treated pure Inconel 718 coating.
• The study shows that the method of forming Inconel 718/MAR-M 002 composite deposits through cold spraying and post-heat-treatment improves the interparticle bond strength in the deposits.

•  Cold spray deposition provides the "possibility of obtaining almost zero-porosity buildups with no theoretical limit to the thickness."
•  Cold spray can also get rid of evaporation, particle melting, crystallization, unwanted oxidation, grain growth, undesirable phases and thermally induced tensile residual stresses.
•  According to research, cold spray technique can be utilized "as a complementary additive manufacturing method for fabrication of high-quality freestanding components where higher deposition rate, larger final size and lower fabrication temperatures are desired."
• According to a report by Arbegast Materials Processing and Joining Lab, the 2 cold spray process system configurations are high-pressure and low-pressure systems.
• One test method used for bond strength or tensile stress in cold spray technique is the ASTM C633 test method, or more specifically the ASTM Standard C 633-01 which uses a tensile testing machine to pull rods and eliminate any forces from bending.
•  ASTM International is a world recognized leader in the delivery and development of voluntary consensus standards, including the cold spray method.
•  ASM Thermal Spray Society, founded in 1994, is a global organization with "approximately 1,500 individuals around the globe representing over 500 leading companies, research institutions and universities."

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