ABSTRACT
This study aims at investigating worn surface topography and mathematical modeling of annealed Ti-6Al-3Mo-2Sn-2Zr-2Nb-1.5Cr alloy using response surface methodology (RSM). The alloy was subjected to three different regimes in order to study their effect on mechanical properties. First regime was applying cold deformation by compression until 15% drop in height at room temperature. The second regime was performing solution treated on the deformed samples at 920 °C for 15 min then air-cooled (AC) to ambient temperature. Third regime was applying aging on the deformed and solution treated specimen for 4 hr at 590 °C followed by air-cooling. Three different velocities (1, 1.5, and 2 m/s) were adopted to conduct dry sliding wear according to the experimental design technique (EDT). Gwyddion and Matlab softwares were used to detect worn surface photographs analytically and graphically. Maximum hardness of 425 HV20 was obtained for AC+Aging specimen, while minimum hardness of 353 HV20 was reported for the annealed specimen. Applying aging process after solution treatment enhanced considerably the wear property and this enhancement reached 98% as compared to the annealed condition. The relationship between input factors (hardness & velocity) and responses (Abbott Firestone zones) was demonstrated using analysis of variance (ANOVA). The best models for Abbott Firestone zones (high peaks, exploitation, and voids) produced accurate data that could be estimated for saving time and cost. The results showed that the average surface roughness increases with increasing sliding velocity for all conditions except AC+Aging condition where the average surface roughness decreased with increasing sliding velocity. The results revealed that at low velocity and hardness, the material gives the highest exploitation zone (86%). While at high velocity and hardness, the material gives the lowest exploitation zone (70%). In general, the predicted results of mathematical model showed close agreement with experimental results, creating that models could be utilized to predict Abbott Firestone zones satisfactorily.
ABSTRACT
Aluminum closed cell foam blocks are created with a volume of 1 inch3 which consist of aluminum foam parts shielded with part of aluminum tube and in some types reinforced with inner aluminum tubes. Blocks have been made to overcome some existing problems in metallic foam used to protect some applications parts from impacts as a sacrificial part. Metallic foam has three main categories sandwich panels, filled tubes and corrugated sheets. Quasi-static compression tests have been applied on 12 blocks with different shapes and compared with pure aluminum foam blocks as a reference. Results display the enhancement of mechanical properties of blocks like yield strength (SY), crushing strength (Sc) and densification strength (Sd), compression at strain 70%, as well as absorbed energy (area of compression under the curve). The highest value for yield strength (5.87 MPa) was registered for Finger phalanxes cube block (FP-0.1 Sq.). While the highest value for densification strength (21.7 MPa) was registered for spine cylinder block (SV8-0.17 C25). The registered results for samples apparent the highest value for energy dissipation density (Edd) is 40.52 J/in3 (91% enhancement) and crushing strength (8.61 MPa) was registered for Finger phalanx cylinder block (FP-0.17 C25). The lowest value for Edd is 14.16 J/in3 (less than pure aluminum foam block value by 33%), SY = 0.42 MPa, Sc = 3.21 MPa, and Sd = 4.46 MPa, registered for thin wall Ear canal cylinder block (EC8-0.075 C26.5). Best mechanical properties had been achieved for Finger phalanx cylinder block (FP-0.17 C25) and spine cylinder block (SV8-0.17 C25).
ABSTRACT
The effects of post heat treatment atmosphere on microstructure and corrosion resistance of duplex stainless steel welded joints were investigated. Post weld heat treatment (PWHT) was carried out with and without protective atmospheres. Nitrogen and argon are used as protective gases individually. Detailed microstructure examination (optical and SEM) demonstrates that nitrides precipitates are highly observed in the welded zones for nitrogen protected samples. An observed drop of ferrite volume fraction in post weld heat treated samples compared with welded samples without heat treatment leading to corrosion resistance enhancement of heat treated welded joints. An exception for using nitrogen as heat treatment atmosphere a decreased corrosion resistance of weldments is investigated due to nitride precipitates. An increase in the weld zone hardness for post weld heat treated samples compared with base alloy. The initial hardness of duplex stainless steel was 286 Hv while average hardness of weld zone was 340, 411, 343, and 391 Hv for as welded, PWHT using air, argon, and nitrogen atmospheres, respectively. Weld zone hardness increased to 33, 44, 20, and 37%. A significant decrease in the ultimate tensile strength and elongation after PWHT. The initial Ultimate tensile strength duplex stainless steel base material was 734.9 MPa while Ultimate tensile strength of the welded joints was 769.3, 628.4, 737.8, and 681.4 MPa for the following conditions: as welded, PWHT using air, argon, and nitrogen atmospheres, respectively.
