Investigating the microstructure and properties of Cobalt base alloy Stellite 6 produced by additive manufacturing process with laser direct metal deposition method.

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Investigating the microstructure and properties of Cobalt base alloy Stellite 6 produced by additive manufacturing process with laser direct metal deposition method.

ارائه دهنده: Provider: salar Hamzehee

اساتید راهنما: Supervisors: Dr Mohsen Sheikhi, Dr Yoosef Mazaheri rodbali

اساتید مشاور: Advisory Professors: Dr. Mahmoud moradi

اساتید ممتحن یا داور: Examining professors or referees: Dr Meysam Nouri, Dr Abbas Pak

زمان و تاریخ ارائه: Time and date of presentation: 2023/03/05, time:13:30

مکان ارائه: Place of presentation: Amphitheater

چکیده: Abstract: In recent years, the process of additive manufacturing with laser has been highly considered as a new solution for the production and repair of metal parts. Having comprehensive information about the microstructural changes and hardness of different areas of the clad sample by changing the process parameters such as: focal distance and laser head to the substrate, laser power, laser scanning direction, and also having a structure free of defects and cracks in the created layers. It is one of the basic requirements of this process. In this research, using direct laser metal deposition method, Stellite 6 alloy was cladded by fiber laser on DIN 1.2714 hot work-grade steel, and the effect of the position of the focal point of the laser beam relative to the surface of the substrate, the distance of the head from the substrate, and the laser power and scanning direction were investigated. At first, 11 single-layer samples were created with a laser power of 250 watts and a variable focal distance from 4 mm above the surface of the substrate to 4 mm below the surface and the distance of the head from the substrate was 15, 17 and 19 mm. The change of these distances on the microstructure and also the hardness were investigated. . Investigations showed that as the focal distance goes from 4 mm above the substrate to 4 mm inside the substrate, the structure becomes finer and it was seen that the hardness also increases and by changing the distance of the nozzle from the substrate from 19 mm above the substrate towards 15 mm from the substrate, the structure is finer and the average hardness is higher. Then, by examining the samples of the single-cladded layer, 5 five-layer samples with powers of 100, 150, 200, 250 and 300 watts with a focal distance of 2 mm above the surface of the substrate were created in the form of bidirectional scanning (reciprocating). The microstructure and hardness were investigated at different points of the samples and it was seen that with increasing laser power from 100 to 300 watts in each sample, the structure became coarser and the average hardness decreased.Then, 3 other samples of five layers, one of which has a power of 250 and a unidirectional scanning direction and a focal distance of 2 mm above the surface of the substrate were created to check the type of scanning direction on the microstructure and hardness of the samples, and two other samples with the same focal distance. And for one-way and two-way scanning, laser power was reduced from 300 to 100 watts in each layer. The purpose of this case was to investigate the type of scanning direction and the power reduction process in each layer on the type of microstructure and hardness of the samples. Investigations showed that the microstructure of bidirectional scanning is more uniform than unidirectional scanning, but its average hardness is lower than unidirectional scanning. Then, the distance of the dendritic arms of the single-layer samples from the three regions of the beginning, middle, and end and of the 5-layer samples in the first to fifth layers was measured in 25 cases in each region, and the average was reported. The distance between the dendritic arms in single-layer samples varies from 1.3 to 3.3 micrometers and in five-layer samples from 1.1 to 4.7 micrometers. Also, in single-layer samples, changing the focal distance led to a change in the dilution of the reference layer in the approximate range of 10 to 90%. Microstructural examination indicated the occurrence of cracking defects in some dilutions. To understand the cause of this phenomenon, one of the solidification crack prediction criteria that was recently proposed was used. This criterion showed that the crack sensitivity increases sharply in the dilution range of 60-90%, which was consistent with the laboratory results. According to this criterion, a sharp increase in the temperature range sensitive to cracking is the cause of cracking in this dilution range.