Influence of Soaking Time on Deep Cryogenic Treatment of CuCoNiBe Alloy

Deep cryogenic treatment (DCT) was investigated at different soaking times to determine the microstructural transformation and mechanical properties of copper beryllium (CuCoNiBe) alloy. Lattice shrinkage/distortion resulting from differences in thermal contraction/expansion between the alpha phase and gamma phase caused internal stress, with large atomic dislocations leading to the formation of beryllides. Average beryllide size decreased with increasing DCT time by a maximum of 37% compared to non-DCT because new small beryllides were formed. Beryllides increased and distributed in the ⍺ phase with longer soaking time. Highest beryllide number and volume fraction found at the longest soaking time of 72 h were approximately 200% and 5%, respectively higher than for non-DCT. Increasing the number of beryllides played an important role in enhancing hardness and wear resistance. Maximal increase in hardness at 12% was observed for 72 h DCT, with reduction in wear volume of 30%. Residual stress as compressive stress showed high variation, with uneven distribution over the DCT sample. Impact strength of the DCT samples decreased by 50%. Analysis of fracture surfaces suggested that beryllide shape and beryllide at the grain boundaries played important roles in reducing fracture resistance. Thermal conductivity measurements of DCT-12 h and DCT-72 h samples indicated microstructural change, with the DCT-72 h sample recording a 2% drop in thermal conductivity compared to non-DCT

Experimental Study of Particles Induced by Screw Tightening Process for Hard Disc Drive Assembly: Effects of ‘Bit’ Speed

The morphology of particles generated during screw tightening process in hard disc drive assembly was studied using a media installing tool kit under a class 100 clean room condition. The screws were made of martensitic 410 stainless steel and the ‘bit’ was made of S2 tool steel. The ‘bit’ speeds used during the screw tightening process can be divided into two steps: the beginning and the final speeds. The effect of both speeds on the morphology of particles generated was investigated. The studied parameters were the aspect ratio and the appearance cross-sectional area of particles. Particles with different sizes were found suggesting that there were different wear mechanisms. Small particles were caused by adhesive wear, while the larger particles were generated by fatigue wear. The appearance cross-sectional area of particles was found to decrease with increase in both speeds within the speed of 250 r/min, after which the appearance crosssectional area appeared to be constant. The effect of cold-weld at asperities was obvious resulting in an increase in aspect ratio at a higher speed. The understanding of the effect of bit speed on the particles morphology during the screw tightening processes could be very useful in the design of the cleaning system in hard disc drive production.The morphology of particles generated during screw tightening process in hard disc drive assembly was studied using a media installing tool kit under a class 100 clean room condition. The screws were made of martensitic 410 stainless steel and the ‘bit’ was made of S2 tool steel. The ‘bit’ speeds used during the screw tightening process can be divided into two steps: the beginning and the final speeds. The effect of both speeds on the morphology of particles generated was investigated. The studied parameters were the aspect ratio and the appearance cross-sectional area of particles. Particles with different sizes were found suggesting that there were different wear mechanisms. Small particles were caused by adhesive wear, while the larger particles were generated by fatigue wear. The appearance cross-sectional area of particles was found to decrease with increase in both speeds within the speed of 250 r/min, after which the appearance crosssectional area appeared to be constant. The effect of cold-weld at asperities was obvious resulting in an increase in aspect ratio at a higher speed. The understanding of the effect of bit speed on the particles morphology during the screw tightening processes could be very useful in the design of the cleaning system in hard disc drive production

Effect of Cryogenic Treatment on the Microstructure Modification of SKH51 Steel

This research aimed to investigate the microstructure modification mechanism used to improve the hardness and wear resistance of SKH51 steel. The cryogenic treatment (CT), including both shallow cryogenic treatment (SCT) and deep cryogenic treatment (DCT), was used to modify the microstructure of SKH51 steel in this research. The effect of short and long holding time (12 and 36 h) in CT was studied. The microstructures were evaluated by using a light optical microscopy (LOM) and a scanning electron microscopy (SEM). The phase identifications of the matrix, carbides, and a-parameter of the matrix were analyzed by using X-ray diffraction (XRD). The M6C and MC carbides size, aspect ratio, and distribution were analyzed using digimizer image analysis software on the SEM micrographs. Micro-Vickers were employed to evaluate the hardness of the targeted samples. Wear tests were performed by using a 6 mm diameter WC ball as the indenter and 5-N-constant load with a ball-on-disk wear tester. The results suggested that the increase of the secondary carbide was caused by the contraction and expansion phenomena of the matrix’s lattice, forcing the carbon atom out and acting as the carbide nucleation. The influence of holding time in the SCT and DCT regions was different. For the SCT, increasing the holding time increased the volume’s fraction of MC carbide. Conversely, the M6C carbide size grew with increasing holding time in the DCT region, while no significant increase in the number of MC carbide was observed. The cryogenic treatment was found to increase the volume fraction of the MC carbide by up to 10% compared to the conventional heat treatment (CHT) condition in the SCT region (both 12 and 36 h) and DCT with 12 h holding time. Due to the microstructure modification, it was found that the cryogenic treatment can improve material hardness and lead to an increase in the wear resistance of SKH51 by up to 70% compared to the CHT treated material. This was due to the increase in the compressive residual stress, precipitation of the MC, and growth of the M6C primary carbide

Performance of a Matrix Type High Speed Steel after Deep Cryogenic and Low Tempering Temperature

A matrix type high speed steel YXR3 designed for a combination of wear resistance and toughness is investigated for its mechanical properties after hardening by deep cryogenic treatment follow by tempering. The deep cryogenic quenching carried out at -200 °C for 36 hours and the single step tempering results in an obvious improvement in wear resistance while balancing the toughness, comparing with the conventional quenching followed by a double tempering treatment. The quantitative image analysis reveals little difference in the MC carbide size distribution between tempering at different temperatures. The synchrotron high energy XRD confirms the MC type carbide with some evolution in its orientation together with tempered martensite approaching the BCC structure at higher temperatures. In contrary to the conventional quenching and tempering, the lowest tempering temperature at 200 °C yields a moderate drop in hardness with increase in surface toughness proportionally while exhibiting exceptional wear resistance. Such thermal cycle can be recommended for the industry both for the practicality and improved tool life