The Laser Institute for Postgraduate Studies has discussed the doctoral dissertation entitled:
“Study of the mechanical properties of Co24.7Cr5W5.4Mo alloy prepared by selective laser melting”
By the student Raghad Ahmed Abdel Razzaq and supervised by Assistant Professor Dr. Ziad Iyad Taha.
Selective laser melting (SLM) is a manufacturing process widely defined as a metal additive manufacturing technique that has the ability to manufacture metal objects and parts with complex and precise geometric shapes. The use of this manufacturing technology has shown promising results in medical applications such as the production of biomedical implants, specifically those manufactured from the cobalt-chromium-molybdenum-tungsten alloy Co24.7Cr5Mo5.4W. One of the necessary conditions when manufacturing materials using SLM technology is to ensure a single product with high mechanical properties. To achieve the proper microstructure and mechanical properties required, it is important to gain a comprehensive understanding of the process control techniques used in experimental SLM.
In the current study, a set of samples were produced by SLM with different operating parameters, where the scanning speed ranged from 700 – 1000 mm/s and the path spacing ranged from 0.06 to 0.08 mm, while other parameters were fixed, such as the laser power at 100 W and the powder layer thickness at 25. μm and build in the zero direction.
The primary goal of the experiments carried out is to evaluate the effect of scanning speed and path spacing on the properties of the manufactured specimens, which included microstructural characteristics, mechanical properties, mechanical corrosion behavior, electrochemical corrosion resistance, surface roughness, and corrosive wear characteristics.
The relative density values ​​of cobalt-chromium-molybdenum-tungsten alloy samples Co24.7Cr5Mo5.4W decreased from 98.2% to 94.4% at 700 mm/s due to increased porosity and reduced laser exposure and at the same speed, the maximum relative density was achieved. Changing track spacing can improve construction speed and reduce relative density.
Samples with different scanning speeds showed varying hardness values, as the hardness values ​​increased with increasing laser scanning speed. The hardness value was 420 HV at the lowest speed of 700 mm/s, while the highest value was 530 HV at 1000 mm/s. The tensile strength of Co24.7Cr5Mo5.4W alloy decreased with the decrease in laser scanning speed due to grain size differences and higher cooling rate. At the low scanning speed of 700 mm/s, the samples recorded the lowest value of the coefficient of friction (COF), which was 0.36, while the value was higher, which was 0.43, at a speed of 1000 mm/s. The scanning speed also affects the tribological properties, which led to the appearance of irregular paths and surface roughness. . It was found that there is a direct relationship between the corrosion resistance of samples and laser scanning speeds, as the Ecorr values ​​recorded for the speeds used in the experiments showed a decrease in the corrosion current density Icorr with the increase in scanning speed from 700 to 1000 mm/s. The sample at scanning speed of 1000 mm/s also showed corrosion wear protective properties due to reduced grain size, enhanced surface abrasion capabilities and formation of a protective layer. This decrease in corrosion potential is closely related to the gradual increase in laser scanning speeds.

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