A. Çelik

Effect of post-oxidizing on tribological and corrosion behaviour of plasma nitrided AISI 5140 steel

Abstract A post-oxidation treatment was performed for times of 15, 30 and 60 min at a substrate temperature of 500 °C to investigate the tribological and corrosion properties of plasma nitrided AISI 5140 steel. The structural, mechanical, tribological and corrosion properties were analyzed by using XRD, SEM, microhardness testing, surface profilometry, pin-on-disk tribotesting and electrochemical polarization. The experimental results showed that oxide layer consists of magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ) phases. With increasing oxidation time, the thickness of the compound layer decreased due to the sputtering as a result of prolonged oxidation. In addition, it was found that the oxidation treatment after plasma nitriding provided an important improvement in the friction coefficient against a WC-Co ball, the wear rate and the corrosion resistance.

Mechanical and structural properties of similar and dissimilar steel joints

The mechanical properties of specimens from similar and dissimilar weld joints were examined. A ferritic steel (St37-2) and an austenitic stainless steel (AISI 304) were joined by the gas tungsten arc weld (GTAW) process using an austenitic filler metal. Mechanical and metallographic properties of the specimens were obtained by means of microhardness testing, tensile testing, bending fatigue testing, and light optical and scanning electron microscopy. The highest microhardness values were recorded on the ferritic-austenitic dissimilar weld joint, whereas the highest tensile strength and bending fatigue life were obtained with the austenitic-austenitic joints. Ferritic and pearlitic structures were observed in the microstructure of the ferritic-ferritic joint. The microstructures of austenitic-austenitic and austenitic-ferritic joints showed small recrystallization grains in addition to the typical austenitic and ferritic structures. Scanning electron microscopy was used to observe the fracture surfaces of the specimens and the origins of the fatigue cracks.

Structural characterization of ion-nitrided AISI 5140 low-alloy steel

The ion nitriding behavior of AISI 5140 alloy steel was investigated under different process parameters including time (1, 4, 8, and 12 h), temperature (400, 450, 500, and 550 � C), and gas mixture ratio (0.05, 0.33, 1, and 3 N2/H2). The ion nitriding of steels has been assessed by evaluation of phase composition, hardness profile, compound layer thickness, and case depth by using a microhardness tester, X-ray diffraction (XRD), and scanning electron microscopy (SEM). It is observed that the compound layer thickness and the case depth increase with increasing treatment time and temperature. With increasing gas mixture ratio, the compound layer thickness increases, whereas the case depth decreases. The maximum surface hardness was observed at 450 � C temperature, for 0.33 N2/H2 gas mixture ratio, and for 4-h treatment time. D 2001 Elsevier Science Inc. All rights reserved.

The investigation of mechanical properties of ion-nitrided AISI 5140 low-alloy steel

Abstract The ion nitriding behavior of AISI 5140 low-alloy steel was investigated under different process parameters including time (1, 4, 8, and 12 h), temperature (400, 450, 500, and 550 °C), and gas mixture ratio (0.05, 0.33, and 3 N2/H2). The ion nitriding properties of AISI 5140 steel have been assessed by evaluating fatigue strength, hardness profile, compound layer thickness, and case depth by using a rotating bending fatigue machine, a microhardness tester, and scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). It was found that ion nitriding improves the fatigue strength, which depends on increasing the case depth, but the compound layer does not have a dominant effect on the fatigue strength. After the fatigue tests, sections of ion-nitrided specimens were observed to have failed by the fish eye phenomenon with the fatigue cracks originating from nonmetallic inclusions.

Determination of the optimum conditions for ion nitriding of AISI 5140 steel

Abstract AISI 5140 low alloy steel was ion nitrided under different process parameters including time (1, 4, 8 and 12 h), temperature (400, 450, 500 and 550 °C) and gas mixture ratio (0.05, 0.33, 1 and 3 N 2 /H 2 ). By determining the fatigue strength, surface hardness, compound layer thickness and case depth, the optimum working conditions were determined by using a Taguchi design of experiment. After ion nitriding process, it is aimed to maximize fatigue strength, surface hardness and case depth as well as to minimize compound layer thickness. While the optimum conditions were determined, due to the goals (above aims) more than one being, the trade-off among goals was considered. First of all, each goal was optimised, separately. Then, all the goals were optimised together, considering the priority of the goals, and the optimum results were obtained at 0.05 N 2 /H 2 gas mixture ratio, at the temperature of 450 °C and for 12 h process time.

Effects of various gas mixtures on plasma nitriding behavior of AISI 5140 steel

AISI 5140 steel was plasma nitrided at various gas mixtures of nitrogen, hydrogen, and argon to investigate the actions of hydrogen and argon on plasma nitriding. The structural and mechanical properties of ion-nitrided AISI 5140 steel have been assessed by evaluating composition of phases, surface hardness, compound layer thickness, and case depth by using X-ray diffraction (XRD), microhardness tests, and scanning electron microscopy (SEM). It was found that the growth of compound layer can be controlled and the diffusion improved when the gas mixture includes H2 gas. Additionally, it was determined that the amount of Ar in dual gas mixture must be at 20% minimum to obtain distinctive surface hardness and compound layer thickness. D 2003 Elsevier Science Inc. All rights reserved.

Wear Behavior of Plasma Oxidized CoCrMo Alloy under Dry and Simulated Body Fluid Conditions

In this study, CoCrMo alloy was oxidized in plasma environment at the temperatures of 600 °C to 800 °C for 1 h to 5 h with 100% O2 gas and its tribological behavior was investigated. After the plasma oxidizing process, the compound and diffusion layers were formed on the surface. XRD results show that Cr2O3, α-Co and ε-Co phases diffracted from the modified layers after plasma oxidizing. The untreated and treated CoCrMo samples were subjected to wear tests both in dry and simulated body fluid conditions, and normal loads of 2 N and 10 N were used. For the sliding wear test, alumina balls were used as counter materials. It was observed that the wear resistance of CoCrMo alloy was increased after the plasma oxidizing process. The lowest wear rate was obtained from the samples that were oxidized at 800 °C for 5 h. It was detected that both wear environment and load have significant effects on the wear behavior of this alloy, and the wear resistance of oxidized CoCrMo alloy is higher when oxide-based counterface is used. The wear rates of both untreated and plasma oxidized samples increase under high loads.

New interlocking intramedullary radius and ulna nails for treating forearm diaphyseal fractures in adults: A retrospective study

INTRODUCTION The treatment goal for diaphyseal forearm fractures in adults is to restore axial and rotational stability. The treatment of these fractures with intrmaedullary locked nailing remains sparse. We therefore evaluated IM nails for treating forearm diaphyseal fractures in adults. METHODS We retrospectively reviewed adult patients with isolated unilateral or bilateral fractures of the radius, ulna, or both, who were treated with closed or mini open reduction with a new IM nail between May 2008 and January 2012 and who were followed for a least 1 year. Patients with a Galeazzi fracture, a pathological fracture or patients with nonunion after previous surgeries were excluded. All patients were allowed full range of motion without any external support. Primary outcomes were Grace and Eversmann rating, Disabilities of the Arm, Shoulder and Hand (DASH) scores. RESULTS The 43 enrolled patients (mean age, 37 years; 32 men) had 59 forearm fractures: 14 isolated radius fractures, 17 isolated ulna fractures (2 bilateral), and 28 fractures of both the radius and ulna. Mean time to fracture union was 13 weeks (range 10-14 weeks) for ulnar fractures and 12 weeks (range 10-13 weeks) for radial fractures. No patient had nonunion, deep infections, or radioulnar synostosis. Followup ranged from 12 to 44 months. Grace and Eversmann ratings were excellent in 38 patients and good in 5. Mean DASH score was 6.5 points (range 0-13.3). CONCLUSIONS Intramedullary nailing of adult forearm diaphyseal fractures appears to be a good alternative to plate osteosynthesis. The advantages are short operative time, minimal invasive techniques, and sufficient stability in all planes that allows early motion without additional fracture support.

Microstructure and structural behavior of ion-nitrided AISI 8620 steel

Abstract The ion nitriding behavior of AISI 8620 alloy steel has been examined under varying process conditions. The process variables included time (1–8 h), temperature (450–600°C) and a 70% H2–30% N2 gas mixture. The structure of the compound layer was studied by X-ray diffraction (XRD) and light optical microscopy. These studies showed that the thickness of the compound layer increased with increasing time at 500°C and 550°C; however, at 600°C, the thickness of the compound layer decreased with increasing time. Phase changes during ion nitriding at 600°C have been investigated using XRD, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS). The maximum surface hardness was obtained at 500°C for 8 h and a larger diffusion layer was obtained at 600°C for 8 h. A braunite layer formed at 600°C.

Mechanical and structural properties of AISI 8620 steel TiN coated, nitrided and TiN coated+nitrided

Abstract The mechanical and structural properties of TiN-coated, plasma-nitrided and TiN coated–nitrided AISI 8620 steel were investigated. The plasma nitriding process was carried out under various conditions of temperature (500°C), time (1, 4, 10 h), and gas mixture (70% N2+30% H2) at 10-mbar working pressure. The titanium nitride coatings were deposited using a closed-field unbalanced magnetron sputtering system (CFUBMS). Nitrided, TiN-coated and TiN+nitrided sample surface were characterized using microhardness tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The highest microhardness (10 gf) was obtained at 500°C for 4 h nitriding time. The alloy nitrides produced (CrN, Mn4N) showed a stable condition at all nitriding times. The adhesion of nitrided+TiN coated sample was obtained at 4 h using a plasma-nitrided process.