Bahadir Uyulgan

Friction and wear properties of Mo coatings on cast-iron substrates

In order to protect machining parts against wear and corrosion in automotive, aerospace, pulp and paper industries, they are coated with Mo-based materials. For these specific applications, Mo coatings were fabricated on cast-iron substrates using an atmospheric plasma-spray system and their friction and wear behavior were evaluated. The Mo coatings were subjected to sliding wear against AISI 303 counter bodies under dry and acid environments. A pin-on-plate type of apparatus was used with normal loads of 49, 89 and 129 N, and sliding speed of 1 Hz. In the steady state, it was demonstrated that the Mo-coated samples under dry conditions had slightly higher wear resistance than under acid conditions tested under a load of 129 N. Several wear failure mechanisms, such as local plastic deformation, cracks, pits, debris, grooves, scratches and tracks, were identified after the tests.

Wear properties of functionally gradient layers on stainless steel substrates for high temperature applications

Abstract Metal substrate components have been coated with functionally gradient coatings (FGCs) to improve thermal barrier properties and heat efficiency of high temperature materials in gas turbine engines, nuclear fusion equipment, diesel engines, jet engines and space shuttles. In this study, functionally graded materials (FGMs), which contain NiCrAl, 75% NiCrAl+25% MgZrO 3 , 50% NiCrAl+50% MgZrO 3 , 25% NiCrAl+75% MgZrO 3 and 100% MgZrO 3 coating layers, have been produced onto stainless steel substrates via an atmospheric plasma-spray technique. The fabricated samples were characterized by means of an optical microscope, scanning electron microscope (SEM), X-ray diffraction and microhardness tester. The wear behaviour of the FGCs was evaluated under dry conditions using a pin-on-plate configuration. The surface morphologies of the FGM samples after wear experiments were examined by SEM. The wear mechanism of the FGCs is discussed based on SEM observation of the worn surface morphologies.

The biomechanical assessment of fixation methods in periprosthetic femur fractures.

OBJECTIVE The aim of our study was to compare the biomechanical properties of different fixation methods used in periprosthetic femur fractures. METHODS We created sawbone models with Mallory Type 2 periprosthetic femur fractures. The periprosthetic fractures were fixed with cables, cables and strut graft, or cables and plates. The biomechanical properties of these three different fixation methods were compared with the intact femur, the intact femur with prosthesis and the femur with periprosthetic fracture without fixation. RESULTS The periprosthetic fracture without fixation had a significantly lower yield point value than the periprosthetic fractures with fixation (p<0.05). There was no significant difference between the three different fixation methods of the periprosthetic fractures. The intact femur with a prosthesis showed statistically higher values than all three fixation methods of perioprosthetic fractures. CONCLUSION Mallory Type 2 periprosthetic fractures should be fixed. There is no difference among the fixation methods used in the study and none of them provide a stability equivalent to that of an intact femur with prosthesis.

An Investigation of Fracture Toughness of Carbon/Epoxy Composites

Fracture toughness of material has a great importance in the determination of the resistance of the material to crack propagation. The starting point in fracture mechanics analysis is to consider a crack of a certain size located in a component or specimen. The pure tensile specimen e.g., SENT (single edge notch tension), have the lowest constraint, while specimens dominated by bending have the highest constraint. In this paper, the woven carbon/epoxy composite material with eight lamina was produced which has a volume fraction of carbon fiber of approximately 60% mechanical properties of this woven composite have been calculated. The fracture toughness value was measured by using the crack mouth opening displacement (CMOD) method experimentally. An experimental investigation has been carried out on the fracture toughness of woven carbon/epoxy composite at room temperature using SENT specimens. The finite element study was carried out by using a 2-D model to obtain the fracture toughness value of woven carbon/epoxy composite numerically with the ABAQUS finite element software package. The result obtained via the CMOD method has been compared with the finite element method (FEM) results. Comparison showed good agreement.

The Biomechanical Effects of Talectomy on the Foot

The biomechanical effects of talectomy on the foot were investigated in seven fresh below-the-knee amputation specimens using pressure-sensitive films placed on the facets of the calcaneus, footprints, and loading-pattern diagrams in the intact foot and after talectomy with anterior and posterior displacement of the foot. Both talectomy techniques distorted the loads carried by the facets of the calcaneus. In the intact foot, 65.6% of the loads were carried by the posterior facet of the calcaneus and 34.4% by the anterior and middle facets. After talectomy with anterior displacement of the foot, although the loads carried by the anterior and middle facets decreased significantly (P = .018), the increase in the loads carried by the posterior facet was not significant compared with the intact foot (P = .176). Similarly, the loads carried by the posterior facet decreased significantly after talectomy with posterior displacement of the foot (P = .028), but the increases in the loads carried by the anterior and middle facets were not significant (P = .735). Comparing the two types of talectomy, the loads carried by each facet changed significantly (P = .018). Talectomy with posterior displacement of the foot also changed the loading patterns and resulted in significant pronation of the foot. These results suggest that talectomy should be performed only as a salvage procedure and that talectomy with anterior displacement of the foot may be preferred when talectomy is indicated.

Wear and Friction Properties of Multilayer Hard Coatings by HTCVD Method

This paper concerns the wear and friction properties of multilayer hard coatings on WC(Ti, Ta, Nb, W)C-Co hard metal substrates for cutting tool applications. The multilayer hard coatings with TiCN+TiC+TiCN+Al2O3+TiN configuration were deposited at the temperatures of 800-1000 o C by using a high temperature chemical vapour deposition (HTCVD) process. The multilayer coatings were characterized by X-ray diffraction, and scanning electron microscopy (SEM). It was found that all multilayer coatings have a dense and homogeneous surface morphology. The multilayer hard coatings (BK-247) with 7.5 μm showed the best wear resistance under 50 N. It as also determined that the Ti-410 specimens with 10.5 μm thick had the best wear resistance at 200 N.

Fracture behavior of various welded steels

Abstract In this study, P295GH (17Mn4) pressure vessel steel and AISI 304 stainless steel were joined by using ER 309L electrodes. Welded specimens were fatigued by four point bending experiments. Cracks occurred on the stainless steel side of the weldment during the fatigue tests. Finite element (FE) analyses were conducted by fixing 2-D precracked model for welded 17Mn4 pressure vessel steel and AISI 304 stainless steel by using ER 309L electrodes. True stress and true strain values of the AISI 304, 17Mn4 steels and ER 309L electrodes were determined by tensile tests. Stress analyses were conducted after entering the linear and nonlinear properties of the materials into software manually. Eventually, fracture mechanics analyses were conducted for the model, and J integral fracture toughness values of the crack on the weldment were calculated.

An in Vitro Wear Investigation of Dental Ceramic Porcelain Veneers

In this study, an in vitro wear behaviour of dental ceramic porcelain veneers was investigated. The ceramic veneers were fabricated on NiCrMo substrate through glazing method. Surface morphology of the veneers was characterized by scanning electron microscopy (SEM). The wear tests were conducted with the porcelain veneers at different loads under in vitro conditions through a pin-on-plate configuration against a human tooth counterbody. The worn surfaces of the porcelain veneers and human tooth counter material were examined by optical microscope. Porcelain veneer samples exhibit higher wear resistance and lower dynamic friction coefficient and wear rate do not change significantly at a given distance up to 100 N of applied load. Introduction Restorations such as hybrid resin composites suffer from a limited longevity, due to the fact that resin composites remain susceptible to discoloration, wear and marginal fractures, reducing thereby the aesthetic result in long term. In search for more durable aesthetics, porcelain veneers have been introduced in the last decade. Glazed porcelain veneers were proposed to be durable for anterior restorations with superior aesthetics [1-3]. In recent decades, significant research has been undertaken in the attempt to improve wear resistance of dental materials. The development of an efficient and effective in vitro wear test therefore has the potential to make a significant impact in dental materials research. In this study, the wear tests were conducted on dental ceramic veneer in vitro condition by using pin-on-plate configuration against human tooth counterbody. The main aim of this study was to compare the wear rates and coefficients of friction of the ceramic veneer. Experimental studies Dental porcelain veneer (Ceramco II) was used as crown material. Materials used for making dental porcelain were plaster, wax, revetment, abraders, varnish, insulator, and porcelain powders and metallic substrates. Ceramic raw materials of the tooth porcelains mainly consisted of clay, kaolin, quartz and feldspar, while commercial dental porcelains were coated on NiCrMo metallic substrate using a glazing process. The coatings were fired at 960 °C for 10 minutes in a vacuum atmosphere. After fabrication of the porcelain veneers, surface morphology of the ceramic porcelain samples was characterized by using SEM. The samples in the form of 5.5 mm in a diameter and 20 mm length were prepared for sliding wear tests. Wear tests were carried out by using a universal wear-friction tester (PLINT TE 88) (pin on plate). The counter material was prepared from human tooth. Tests were performed with normal load of 50, 100 and 150 N. The tests were performed at a sliding speed of 0.3 Hz with a stroke length of 8 mm. Samples were subjected to wear for 7200 s. After each test, wear rates and coefficients of friction of the ceramic veneer samples were determined. The worn surfaces of the human tooth counter material were examined by optical microscope. Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2005-2008 doi:10.4028/www.scientific.net/KEM.264-268.2005