Effect of Boronizing on Operating Stability of Steel AISI 304L under Erosion Impact of Hard Particles

Metal Science and Heat Treatment - The effect of solid boronizing at 950°C for 2 and 4 h on the phase composition, microstructure, hardness and abrasive wear of steel AISI 304L is studied...     

Influence of T5 heat treatment on the microstructure and lubricated wear behavior of ternary ZnAl40Cu2 and quaternary ZnAl40Cu2Si2.5 alloys

A ternary ZnAl40Cu2 and a quaternary ZnAl40Cu2Si2.5 alloys were produced by permanent mold casting and subjected to T5 heat treatment at a temperature of 150 °C for 24 hours. The structural, mechanical and lubricated wear properties of these alloys were investigated in the as-cast and heat-treated conditions and the results were compared with those of SAE 65 (CuSn12) plain bearing bronze. Microstructure of the ternary alloy consisted of aluminum-rich α, eutectoid conversion product of α+η and ϵ phase located in the interdendritic channels. In addition to these phases, silicon particles were observed in the microstructure of the quaternary alloy. T5 heat treatment caused a considerable amount of reduction in the hardness, tensile strength and wear resistance of ZnAl40-based ternary and quaternary alloys, but improved their ductility and stability. These alloys in the as-cast and heat-treated conditions exhibited lower wear volume or higher wear resistance than SAE 65 bearing bronze. Among the experimental alloys, the optimum mechanical properties and wear performance were obtained from ZnAl40Cu2Si2.5 alloy in both as-cast and heat-treated conditions. Adhesion appeared to be the main wear mechanism for the ZnAl40-based alloys, but abrasion dominated the wear of SAE 65 bronze.     

Symbolic decision procedure for termination of linear programs

Tiwari proved that the termination of a class of linear programs is decidable in Tiwari (Proceedings of CAV’04. Lecture notes in computer science, vol 3114, pp 70–82, 2004). The decision procedure proposed therein depends on the computation of Jordan forms. Thus, people may draw a wrong conclusion from this procedure, if they simply apply floating-point computation to compute Jordan forms. In this paper, we first use an example to explain this problem, and then present a symbolic implementation of the decision procedure. Thus, the rounding error problem is therefore avoided. Moreover, we also show that the symbolic decision procedure is as efficient as the numerical one given in Tiwari (Proceedings of CAV’04. Lecture notes in computer science, vol 3114, pp 70–82, 2004). The complexity of former is max{O(n ⁶), O(n ^m+3)}, while that of the latter is O(n ^m+3), where n is the number of variables of the program and m is the number of its Boolean conditions. In addition, for the case when the characteristic polynomial of the assignment matrix is irreducible, we design a more efficient symbolic algorithm whose complexity is max(O(n ⁶), O(mn ³)).     

Effect of fiber orientation on interfacial fracture toughness for adhesively bonded composite plates

In this study, interfacial fracture toughness was investigated experimentally and numerically in laminated composite plates with different fiber reinforcement angles bonded with adhesive. The composite plates are four-layered and the layer sequence is [0º/θ]_s. DCB test was applied to composite plates reinforced with epoxy resin matrix and unidirectional carbon fiber. The experimental sample model for the DCB test was made using the ANSYS finite element package program. In the numerical study, four layered composites were prepared in three dimensions. Under critical displacement value; mode I fracture toughness at the crack tip was calculated using VCC (virtual crack closure) technique. Numerical values consistent with experimental results have presented in graphical forms. At 60o and 75° the greatest fracture toughness was obtained. In addition, numerical results have shown that fiber orientation prevents the uniform distribution of stress on the interface crack tip and causes stress accumulation, especially at the edge of the plate.

     

Partial characterization of peptides from emmentaler cheese

A novel isolation procedure for the identification of casein breakdown products in Swiss‐type cheese is described. The cheese extracts were cleaned‐up and fractionated on Waters Sep‐Pak C₁₈ and ion‐exchange (CM‐ and QMA‐Plus) cartridges. The advantages of this preparation technique are discussed. Peptides of different physico‐chemical nature were analyzed by RP‐HPLC. The sequence assays of characteristic segments of the peptide spectrum were carried out by HPLC‐analysis of the phenylthiocarbamyl amino acid derivatives and by automated Edman‐degradation. This experimental approach holds promise for the characterization of the cheese ripening process. Relationships between casein peptides and flavor development are proposed. The results obtained suggest that changes in casein peptides do not parallel the development of cheese flavor. The sequences of six predominant basic peptides are presented. It is the first report on the sequence of protein degradation products in Swiss cheese.     

Influence of Test Conditions on the Lubricated Friction and Wear Behaviour of Al–25Zn–3Cu Alloy

The friction and wear properties of Al–25Zn–3Cu alloy were investigated over a range of oil flow rate, pressure and sliding speed using a pin-on-disc machine, after examining its microstructure and mechanical properties. The results obtained were compared with those of a conventional-bearing material (SAE 65 bronze). It was observed that the microstructure of the Al–25Zn–3Cu alloy consisted of aluminium-rich α, eutectoid α + η and θ phases, while the microstructure of the SAE 65 bronze revealed copper-rich α, and eutectoid α + δ phases. It was found that the friction coefficient, temperature and wear volume of both the alloys decreased sharply with increasing oil flow rate and attained almost constant levels beyond a certain range of oil flow rate. It was also found that the friction coefficient and the wear volume of the alloys decreased with increasing pressure, but was observed to be almost independent of the sliding speed. The Al–25Zn–3Cu alloy exhibited higher wear resistance as compared to that of the bronze under all the test conditions. Smearing type of adhesion appeared to be the most effective wear mechanism for the Al–25Zn–3Cu alloy, while abrasion dominated one for the SAE 65 bronze.     

Termination of linear programs with nonlinear constraints

Tiwari (2004) proved that the termination problem of a class of linear programs (loops with linear loop conditions and updates) over the reals is decidable through Jordan forms and eigenvector computation. Braverman (2006) proved that it is also decidable over the integers. Following their work, we consider the termination problems of three more general classes of programs which are loops with linear updates and three kinds of polynomial loop conditions, i.e., strict constraints, non-strict constraints and both strict and non-strict constraints, respectively. First, we prove that the termination problems of such loops over the integers are all undecidable. Then, for each class we provide an algorithm to decide the termination of such programs over the reals. The algorithms are complete for those programs satisfying a property, Non-Zero Minimum.     

Developing aluminium–zinc-based a new alloy for tribological applications

In order to develop aluminium–zinc-based a new alloy for tribological applications, six binary Al–Zn and seven ternary Al–25Zn–(1–5)Cu were prepared by permanent mould casting. Their microstructure and mechanical properties were investigated. Dry sliding friction and wear properties of the ternary alloys were investigated using a pin-on-disc machine. Surface and subsurface regions of the wear samples were studied with scanning electron microscopy (SEM). The highest hardness and tensile strength were obtained with the Al–25Zn alloy among the binary ones. The microstructure of this alloy consisted of aluminium-rich α and eutectoid α + η phases. Addition of copper to this alloy resulted in the formation of θ (CuAl₂) phase. The hardness of the ternary alloys increased with increasing copper content. The highest tensile and compressive strengths and wear resistance and the lowest friction coefficient were obtained from the ternary Al–25Zn–3Cu alloy. The dimensional change measured on ageing (stabilization) of this alloy was found to be much lower than that obtained from the copper containing zinc-based alloys. Microstructural changes were observed below the surface of the wear samples of the Al–25Zn–3Cu alloy. These changes were related to the heavy deformation of the surface material due to normal and frictional forces, and smearing and oxidation of wear material. Adhesion was found to be the main wear mechanism for the alloys tested.     

The Effect of Solid Boriding Time on the Structure,Hardness and Corrosion Properties of AISI 5140 Steel

Protection of Metals and Physical Chemistry of Surfaces - In this study, AISI 5140 steel samples were borided in an electrical furnace at a temperature of 950°C for 4, 6 and 8 h. Structural...     

Dry Sliding Friction and Wear Properties of Al–25Zn–3Cu–(0–5)Si Alloys in the As-Cast and Heat-Treated Conditions

Dry sliding friction and wear properties of ternary Al–25Zn–3Cu and quaternary Al–25Zn–3Cu–(1–5)Si alloys were investigated using a pin-on-disc test machine after examining their microstructures and mechanical properties. An alloy (Al–25Zn–3Cu–3Si), which exhibited the highest tensile and compressive strengths, was subjected to T7 heat treatment. Surface and subsurface of the wear samples were investigated using scanning electron microscopy (SEM). The hardness and both tensile and compressive strengths of the alloys increased with increasing silicon content, but the trend reversed for the latter ones above 3% Si. It was observed that T7 heat treatment reduced the hardness and both tensile and compressive strengths of the Al–25Zn–3Cu–3Si alloy, but increased its elongation to fracture greatly. Three distinct regions were observed underneath the surface of the wear samples of the Al–25Zn–3Cu–3Si alloy. The formation of these regions was related to the heavy deformation of surface material and mixing, oxidation and smearing of wear material. Al–25Zn-based ternary and quaternary alloys in both as-cast and heat-treated conditions were found to be superior to SAE 660 bronze as far as their mechanical and dry sliding wear properties are concerned.