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The pulverizer blade in food and animal feed production is subjected to abrasive wear from agricultural produce such as millet, corn, beans, rice husk and hull, resulting in the contamination of food by the wear debris from the blade material. This work compares different surface treatment and coating techniques used in improving the abrasive wear resistance of the blade, thus reducing the amount of contaminant. Four types of pulverizing blades were tested, namely flame hardened blade, hard Cr plated blade, plasma-sprayed Al 2 O 3 -TiO 2 coated blade and HVOF-sprayed WC–Co coated blade. The dry abrasive wear test was carried out in a lab scale pulverizing test rig using rice husk as the abrasive media. The wear result, reported as the reduced area of the leading face, shows that the hard Cr plated-, Al 2 O 3 –TiO 2 coated- and WC–Co coated blades display similar wear rates, which is lower than that of the flame hardened blade. When the weight loss of the blade was calculated from the wear volume and density of each blade, it was found that the Al 2 O 3 –TiO 2 coated blade exhibits significantly lower weight loss due to its low density, rendering a lower mass of contaminant being released into the produce. The weight losses of the blades fitted in the inside position after 40 h of pulverizing test are 8.4, 3.7, 1.6 and 4.8 mg per one blade for flame hardened blade, hard Cr plated blade, Al 2 O 3 –TiO 2 coated blade and WC–Co coated blade, respectively. These values were used to estimate the contaminant concentrations in rice husk.

Stainless steel/carbon nanotube (SS/CNT) composite coating was prepared by thermal spray from the feedstock powder synthesized by chemical vapor deposition at a synthesis temperature and time of 800 °C and 120 min under ethanol atmosphere. Microstructural investigation by TEM and SEM revealed that grown CNTs covering the surface of stainless steel particles were multi-walled type with an average diameter of about 44 nm. Microstructures of pure stainless steel and SS/CNT composite coatings similarly showed splat characteristic and lamellar structure. Incorporation of CNTs was clearly observed in the composite coating. Hardness of SS/CNT composite coating (480 ± 36 HV0.3) was higher than that of pure stainless steel coating (303 ± 33 HV0.3). Coefficient of friction of the SS/CNT coating was almost 3 times lower than that of stainless steel coating which resulted in reduction of sliding wear rate of nearly 2 times. This research thus demonstrated a new composite coating with better wear resistive performance compared to a coating deposited by commercially available stainless steel powder.

NiCrBSi is a material popularly used as a hard thermal sprayed coating. The coating performs well as a wear resistant coating under low stress. At higher stress in metal-to-metal sliding wear condition, however, the NiCrBSi starts to experience surface deformation, which will inevitably lead to seizure as the stress increases. In order to improve the tribological properties of the NiCrBSi plasma-sprayed coating, Mo is added to the coating to reduce the friction between the coating and other metal contacting surface, thus, improving its dry sliding wear resistance. In this study, various amounts of Mo were mixed with NiCrBSi at 0, 25, 50, 75 and 100 wt.%. The powders were sprayed using an air plasma spraying technique onto stainless steel samples to form coatings, which were ground to achieve flat surfaces and a thickness of 350–400 μm. The mechanical properties of the coatings were determined. The coating samples were then tested using a reciprocation ball-on-flat tribometer. It was found that as the Mo/NiCrBSi ratio increases, the wear mechanism changes. Coatings containing 75%Mo and 25%NiCrBSi exhibit the highest wear depths corresponding to the cracking of the thin NiCrBSi splats. On the other hand, coatings containing 25%Mo and 75%NiCrBSi possess the lowest wear depths with no surface cracks. The presence of Mo covering the coating surface hinders the metal seizure between NiCrBSi and steel counter surface.

Al2O3/xTiO2 (where x = 0, 3, 13 and 20 wt%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed micron-sized Al2O3 and nano-sized TiO2 powders. Phase transformation from mainly stable α-Al2O3 and anatase-TiO2 in the powders to predominant metastable γ-Al2O3 and rutile-TiO2 in the coatings was observed. Reaction between Al2O3 and TiO2 phase also occurred producing Al2TiO5 phase. Microstructural investigation showed that well separated TiO2 lamellas were homogeneously dispersed between Al2O3 lamellas. Hardness was found to decrease with increasing TiO2 content while fracture toughness increased. The average wear rates of composite coatings determined by sliding wear test were lower than that of monolithic Al2O3 coating by approximately 40%. This was mainly attributed to an increase in fracture toughness and reduction of friction coefficient due to a presence of TiO2 splats.

The oxidation dynamics of an overlay coating and the corresponding thermal barrier coating system are presented. The particular systems examined are composed of a nickel-based superalloy with an air plasma-sprayed NiCrAlY bond coat and the thermal barrier coating system consists of air plasmasprayed yttria stabilized zirconia layer. Failure can occur in these systems by crack propagation within the ceramic outer layer at the interface with the bond coat. Defects, such as microcracks and pores, are common in plasma-sprayed coatings and within the thermally grown oxide scales. These can act as initiation sites for cracks. The subsequent growth of these cracks can lead to loss of the outer protective materials. Considerable information is available by microscopic examination of sections through test specimens that have been held at temperature for varying amounts of time. By careful sample preparation it is possible to monitor the development of the oxide scale formed during high temperature testing ...

The use of a conventional air plasma-sprayed thermal barrier coating (TBC) and a porous, functionally graded TBC as a thermal insulator for Al7075 alloy was explored. A quench test at 1200°C employing fast heating and cooling rates was setup to represent a dynamic thermal condition of an aerospace component. During the test, coated samples were subjected the ambient temperature of 1200°C for a very short time. This was followed by a rapid drop in temperature resulting in cracking of the coatings. For the conventional TBC, it was found that the temperature of the Al7075 substrate decreases with the increase in the ZrO2 topcoat thickness. However, at the topcoat thickness of 1100 µm, large horizontal cracks can be observed in the topcoat and at the topcoat thickness of 1600 µm, the topcoat delaminate during cooling after the quench test. The porous, functionally graded TBC with 600 µm thick topcoat, on the other hand, was found to be as effective at reducing the substrate temperature as the conventional TBC with 1100 µm thick topcoat. The maximum substrate temperature is about 213°C for the former and 208°C for the latter when a heating rate of 38°C/s was used. When the quench tests were conducted with a faster heating rate of 128°C/s, the Al7075 substrate heat up faster with a reduction in the maximum substrate temperatures. The substrate temperatures dropped from 297 to 212°C for the conventional TBC and from 213 to 155°C for the porous TBC, both with 600 µm thick topcoat. Segmentation cracks were observed in both coating after the quench test., {"references":["P. E. Magnusen, R. J. Bucci, A. J. Hinkle, J. R. Brockenbrough and H. J.\nKonish, \"Analysis and prediction of microstructural effects on long-term\nfatigue performance of an aluminum aerospace alloy\", Int. J. Fatigue\nVol. 19, (1997) S275–S283.","M. S. 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This paper presents the optimal design of PID controller based on a particle swarm optimization (PSO) approach for position control using spring shape memory alloys (SMA) actuator. The mathematical model of experimental system had been approximate near the operating point for the PSO algorithm to adjust PID parameters for the minimum integrated absolute error (IAE) condition. The results show the adjustment of PID parameters converting into the optimal point and the good control response base on the optimal values by the PSO technique.

Thermal barrier coating (TBC) is applied on a surface of a gas turbine blade to provide a thermal barrier and oxidation resistant properties for the components. The ability to resist oxidation of the coating arises from the self-healing, protective Al2O3 scale on top of the bondcoat, which is formed during service. However, if Al depletion occurs within the coating, the protective scale will lose its self-healing ability, and hence, its oxidation resistant property. This paper investigated the depletion of Al within the bondcoat by studying the microstructure of the bondcoat on a gas turbine blade after it has been in 4,000 hour service at 1,200°C. The results showed that Al depletion had occurred at a different level throughout the turbine blade. In the area where Al depletion had not yet occurred, precipitation of a (Ni,Al)-rich phase was detected. Most of the Al was contained within this phase, leaving only small amount of Al in the surrounding matrix. A well-defined boundary was observed between the depleted and non-depleted regions.