MODE INFLUENCE OF SELECTIVE LASER IMPACT UPON  POROSITY OF SAMPLES OF COBALT, CHROMIUM  AND MOLYBDENUM POWDERS

The purpose of this investigation consists in the analysis of possibility to obtain products by means of the SLP method using powders of cobalt, chromium and molybdenum having considerable difference in melting temperatures of cobalt (1768ºC), chromium (2130ºC) and molybdenum (2890ºC), density, thermal conduction and solving for the optimum technological modes of powder composition melting to obtain samples with lower porosity. The investigation methods include methods of physical material science. Investigation results and novelty: a procedure for obtaining a powder composite of the cobalt-chromium-molybdenum system for selective laser melting is developed. There are carried out experimental investigations on the selection of optimum technological modes for the layer-by-layer laser melting of a cobalt-chromium-molybdenum alloy of powder composition. A method for layer-by-layer laser synthesis for the solution of a principle matter – possibility for the synthesis of the products of cobalt chromium and molybdenum powders having a considerable difference in melting temperatures, density, heat conductivity and so on. The investigations of model alloy samples of cobalt-chromuim-molybdenum system obtained through the method of layer-by-layer laser synthesis on optimized technological modes through the methods of scanning electronic microscopy allow defining sample porosity. The generalization of obtained numerical and experimental investigation results and definition of essential conditions for selective laser melting allow optimizing modes and parameters of the synthesis. Conclusions: the optimum modes of selective laser melting for obtaining the samples with the powder composition of 66 mas. % Co, 28 mas. % Cr, 6 mas.% Mo through the method of selective laser melting with minimum porosity are: laser capacity P=100Wt, scanning rate v=350mm/s, modulation 5000Hz, scanning pitch s=0.1mm, layer thickness h=0.03mm, melting process takes place in protective argon environment.

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Surface Formation Mechanisms in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.839.73 ◽

2020 ◽

Vol 839 ◽

pp. 73-78

Author(s):

Alexander A. Saprykin ◽

Yuriy P. Sharkeev ◽

Natalya A. Saprykina ◽

Egor A. Ibragimov

Keyword(s):

Selective Laser Melting ◽

Marangoni Effect ◽

Powdered Material ◽

Formation Mechanisms ◽

Cobalt Chromium ◽

Laser Melting ◽

Movement Velocity ◽

Surface Formation ◽

Preheating Temperature ◽

Cobalt Chromium Molybdenum

Selective laser melting (SLM) is a manufacturing technology of metal parts of any shapes with target mechanical properties by means of laser melting. This paper discusses the effect of SLM parameters: laser output power, laser movement velocity, scanning pitch and preheating temperature of a powdered material on surface formation mechanism, namely, its physical configuration when melting cobalt-chromium-molybdenum powdered material Со28Cr3Mo. The study points at structural differences of melted surfaces even under identical process parameters. Several types of surface formation are identified, e.g. homogenous melt, coagulated particles, and shapeless particles. Vapor pressure, Marangoni effect, and heat effect of a melted powder are stated to be key reasons for rough surface. This research is of high importance for understanding the effect of SLM parameters on formation of a target quality surface, positive stability and repeatable accuracy of the process.

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An Experimental Study on Micro-Milling of a Medical Grade Co-Cr-Mo Alloy Produced by Selective Laser Melting

Materials ◽

10.3390/ma12132208 ◽

2019 ◽

Vol 12 (13) ◽

pp. 2208 ◽

Cited By ~ 11

Author(s):

Gabriele Allegri ◽

Alessandro Colpani ◽

Paola Serena Ginestra ◽

Aldo Attanasio

Keyword(s):

Additive Manufacturing ◽

Selective Laser Melting ◽

Chip Thickness ◽

Material Behavior ◽

Micro Milling ◽

Cobalt Chromium ◽

Laser Melting ◽

Chip Formation Mechanism ◽

Manufacturing Techniques ◽

Cobalt Chromium Molybdenum

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this field, micro-milling can be used for the creation of micro-scale details on the printed parts, not obtainable with Additive Manufacturing techniques. In particular, there is a lack of scientific research in the field of the fundamental material removal mechanisms involving micro-milling of Co-Cr-Mo alloys. Therefore, this paper presents a micro-milling characterization of Co-Cr-Mo samples produced by Additive Manufacturing with the Selective Laser Melting (SLM) technique. In particular, microchannels with different depths were made in order to evaluate the material behavior, including the chip formation mechanism, in micro-milling. In addition, the resulting surface roughness (Ra and Sa) and hardness were analyzed. Finally, the cutting forces were acquired and analyzed in order to ascertain the minimum uncut chip thickness for the material. The results of the characterization studies can be used as a basis for the identification of a machining window for micro-milling of biomedical grade cobalt-chromium-molybdenum (Co-Cr-Mo) alloys.

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Formation of Structural-Phase State in a Cobalt-Chromium-Molybdenum Alloy by Selective Laser Melting

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.313.50 ◽

2021 ◽

Vol 313 ◽

pp. 50-58

Author(s):

A.A. Saprikin ◽

Yurii P. Sharkeev ◽

Natalya A. Saprykina ◽

Margarita A. Khimich ◽

Egor A. Ibragimov

Keyword(s):

Low Temperature ◽

Selective Laser Melting ◽

Mechanical Engineering ◽

Stable Phase ◽

Temperature Phase ◽

Cobalt Chromium ◽

Laser Melting ◽

Machine Parts ◽

Cobalt Chromium Molybdenum ◽

Low Temperature Phase

Heat resistant cobalt-based alloys have found a specific niche in the present-day mechanical engineering due to their unique properties. To begin with, cobalt-based alloys are used as corrosion, heat and wear resistant materials intended for aggressive environments and operation at extreme temperatures, e.g. blades, nozzles, swirlers, rings and other elements of turbines and internal combustion engines. Traditional molding methods applied in the mechanical engineering fail to provide necessary operational and technological characteristics of aforementioned machine parts. Owing to selective laser melting it is possible to reduce a production time and manufacturing costs for machine elements with a complex physical configuration and generate an alloy with an extraordinary structure, which is not found in traditionally combined compounds. A structure of cobalt exists in two crystal modifications: a hexagonal close-packed epsilon phase, a low-temperature phase and a face-centered cubic lattice gamma phase, a high-temperature phase. The alloy hardness is directly related to an amount of a low-temperature phase. The laser melting shortens a laser beam impact time on a powder composition due to a higher power and laser travelling speed. A high value of heat conductivity seems to be the reason for rapid solidification and cooling, which, in their turn, increase a percent of an alpha-martensite phase in an alloy and improve the hardness and wear resistance of machine parts. The reported paper summarizes studies aimed at the development of a stable phase structure three-component alloy (Сo-66 mass % Cr-6 mass % Mo) based on the cobalt-chromium-molybdenum system and mixed up via selective laser melting.

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The Mechanism of Forming Coagulated Particles in Selective Laser Melting of Cobalt-Chromium-Molybdenum Powder

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.839.79 ◽

2020 ◽

Vol 839 ◽

pp. 79-85 ◽

Cited By ~ 1

Author(s):

Alexander A. Saprykin ◽

Yuriy P. Sharkeev ◽

Natalya A. Saprykina ◽

Egor A. Ibragimov

Keyword(s):

Selective Laser Melting ◽

Powdered Material ◽

Beam Diameter ◽

Molybdenum Powder ◽

Cobalt Chromium ◽

Laser Melting ◽

Movement Velocity ◽

Scanning Velocity ◽

Preheating Temperature ◽

Cobalt Chromium Molybdenum

Selective laser melting (SLM) is thought to be a prospective manufacturing technology of complex metal components. Formation of coagulated particles when melting is reported to be an important factor for target mechanical properties of the end product. This paper discusses the effect of SLM parameters, including laser output power, laser movement velocity, preheating temperature of the powder, laser beam diameter on the mechanism of forming coagulated particles in melting cobalt-chromium-molybdenum powdered material. The study shows that a rise of power to 60 W at a scanning velocity 6 mm/s causes coagulated particles to expand to 350 μm; that is far bigger than a size of powder in as delivered state (90 μm). The work investigates the effect of mechanical activation of cobalt-chromium-molybdenum powder on dimensions of coagulated particles. The research data can be applied to the improvement of up-to-date optimization approaches to manufacturing process parameters in SLM technology.

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