Influence of nitriding on corrosion resistance of martensitic X17CrNi16‐2 stainless steel

Nitriding increases surface hardness and improves wear resistance of stainless steels. However, nitriding can sometimes reduce their corrosion resistance. In this paper, the influence of nitriding on the corrosion resistance of martensitic stainless steel was investigated. Plasma nitriding at 440 °C and 525 °C and salt bath nitrocarburizing were carried out on X17CrNi16‐2 stainless steel. Microhardness profiles of the obtained nitrided layers were examined. Phase composition analysis and quantitative depth profile analysis of the nitrided layers were preformed by X‐ray diffraction (XRD) and glow‐discharge optical emission spectrometry (GD‐OES), respectively. Corrosion behaviour was evaluated by immersion test in 1% HCl, salt spray test in 5% NaCl and electrochemical corrosion tests in 3.5% NaCl aqueous solution. Results show that salt bath nitrocarburizing, as well as plasma nitriding at low temperature, increased microhardness without significantly reducing corrosion resistance. Plasma nitriding at a higher temperature increased the corrosion tendency of the X17CrNi16‐2 steel.     

Auftraglöten zum Verschleißschutz von Titanwerkstoffen

Wear Protection of Titanium using Surface Brazing Titanium and titanium alloys possess high specific strengths up to a temperature of about 600 °C in addition to an extraordinary corrosion resistance [1]. The low wear resistance constitutes a crucial impediment for a much broader use. Titanium materials are especially susceptible to friction fatigue and erosion. Coating techniques have to be developed in order to counteract this technical constraint. Surface brazing presents a promising approach. Hard metals mixed with brazing filler metals on a silver and titanium basis were brazed in a vacuum furnace and subsequently characterized. Wear resistance was quantified and optimized using ball on disc measurements.     

Rezyklieren von metallischen Spänen mittels Electro‐Discharge Sintering

Composite material Ferro‐Titanit^® is produced powder‐metallurgical by Deutsche Edelstahlwerke GmbH (DEW) and is commonly used for wear and corrosion resistant component parts. Materials properties can be attributed to the microstructure which consists of a corrosion resistant metallic matrix and a huge amount of approx. 50 vol.% of hard Ti‐monocarbides. Although Ferro‐Titanit^® possesses a high amount of hard particles, the material can be machined by turning and drilling in solution annealed condition. Due to the alloying content (Mo, Cr, TiC) of Ferro‐Titanit^®, there is a high motivation to recover those elements by a recycling process of the chips, thus expensive and limited resources can be saved. On idea of a recycling process can be found in the redensification of those chips by electro discharge sintering (EDS). In this work, chips of the material Ferro‐Titanit^® were densified by EDS technique and the resulting microstructure was investigated by optical and scanning electron microscopy. Furthermore, microstructure and hardness of the EDS densified specimens was discussed with regard to the microstructure of conventionally sintered Ferro‐Titanit^®‐samples in laboratory conditions.     

Influence of the microstructure on the corrosion resistance of plasma‐nitrided austenitic stainless steel 304L and 316L

Austenitic stainless steels are widely used in medical and food industries because of their excellent corrosion resistance. However, they suffer from weak wear resistance due to their low hardness. To improve this, plasma nitriding processes have been successfully applied to austenitic stainless steels, thereby forming a thin and very hard diffusion layer, the so‐called S‐phase. In the present study, the austenitic stainless steels AISI 304L and AISI 316L with different microstructures and surface modifications were used to examine the influence of the steel microstructure on the plasma nitriding behavior and corrosion properties. In a first step, solution annealed steel plates were cold‐rolled with 38% deformation degree. Then, the samples were prepared with three kinds of mechanical surface treatments. The specimens were plasma nitrided for 360 min in a H₂–N₂ atmosphere at 420 °C. X‐ray diffraction measurements confirmed the presence of the S‐phase at the sample surface, austenite and body centered cubic (bcc)‐iron. The specimens were comprehensively characterized by means of optical microscopy, scanning electron microscopy, glow discharge optical emission spectroscopy, X‐ray diffraction, surface roughness and nano‐indentation measurements to provide the formulation of dependencies between microstructure and nitriding behavior. The corrosion behavior was examined by potentio‐dynamic polarization measurements in 0.05 M and 0.5 M sulfuric acid and by salt spray testing.     

Mechanical Properties and Corrosion Resistance of Nitrided or Oxinitrided,and Powder Painted Regular and Interstitial Free (IF) Drawing Steel Sheet

Specimens of 0.8 mm thick regular and interstitial free (IF) drawing steel sheet have been nitrided in fluidised bed for 2 hours at 620 °C and 560 °C with and without a post‐oxidation, and slow and accelerated cooling. As a result, surface hardness, yield and tensile strength of the sheets increased considerably without a critical loss of ductility. Resistance welds between the sheets did not lose their original strength after nitriding‐oxinitriding. Nitrided‐oxinitrided at 620 °C and then powder painted sheets, as compared with powder painted raw sheets, were more corrosion resistant in neutral salt spray and climatic tests. Some mechanical and anticorrosion properties of the IF steel sheet that had undergone the nitriding‐oxinitriding processes were definitely better than those of equally processed regular steel sheet.     

Methoden zur mechanischen Charakterisierung von modifizierten Implantatoberflächen in der Orthopädischen Chirurgie

Methods for the mechanical characterisation of modified implant surfaces in orthopaedic surgery Nowadays, on average approximately 10 % of all hip and knee endoprostheses have to be exchanged within the first 10 years. Implant revision is often necessary following aseptic or septic loosening. Hence, today implants for orthopaedic surgery are increasingly being coated for better osseointegration. Coatings have to be biocompatible and meet high mechanical requirements, whereby the adhesive strength and the abrasive wear resistance of the coatings take on a key role. This study presents different methods to asses these parameters experimentally using two innovative coatings (TiN, TiO2‐Cu) exemplary. The adhesive bonding strength of the coatings was investigated using different standardised methods, such as the arbour bending test, scratch test and the standard adhesive test. Wear resistance was determined after 1.5 million cycles in a special testing machine. The investigations showed for both coatings, TiN and TiO2‐Cu, good adhesive strength and wear resistance. The adhesive strength and wear resistance of bio‐active, wear reducing or anti‐allergenic surface coatings can be determined reliably using the above‐mentioned methods.     

Investigation of the properties of nickel-boron/nano-diamond composite coatings upon pre/post heat treatment

The study has explored the physical and chemical properties of nickel-boron/nano-diamond composite coatings upon pre/post heat treatment. The nano-composite coatings were produced by electroless plating. In fact, the effects of using the nano-diamond additives (0 g l⁻¹, 0.1 g l⁻¹, 0.3 g l⁻¹, 0.5 g l⁻¹, 0.7 g l⁻¹) were investigated in pre/post heat treatment. According to the results, the micro-hardness of the nickel-boron/nano-diamond composite coating produced in the bath containing 0.5 g l⁻¹ nano-diamond additive reached to 1005 HV 0.05 upon post-heat treatment. Also, the corrosion resistance of the nickel-boron/nano-diamond composite coatings was modified by using the nano-additive or heat treatment. But, adding nano-diamond particles reduced the ductility and wear resistance of the nickel-boron coatings. We also found, modification of the properties (ductility and wear resistance) of the composite coatings was achieved by using the heat treatment.     

Effect of heat treatment on the corrosion resistance and mechanical properties of selective laser melting Ti6Al4V alloy

The present work shows that the effect of several heat treatments on the corrosion resistance and mechanical properties of Ti6Al4V processed by selective laser melting (SLM). The microstructure of Ti6Al4V alloy produced by selective laser melting exhibited bulky prior β columnar grains, and a large amount of fine acicular martensites α′ were observed inside the prior β columnar grains. The acicular martensitic α′ were transformed to a mixture of α and β after heat treatment, and the grain size increases with the increase of heat-treated temperature. The results of 3.5 wt% NaCl solution electrochemical corrosion test showed that the heat-treated samples possess a higher corrosion resistance than the as-received sample. Among of them, the sample after heat-treated at 730 °C exhibited best corrosion resistance and excellent fracture strain. The sample heat treated at 1015 °C showed worst mechanical properties due to the formation of Widmanstätten structure.     

Effect of tempering temperature on microstructure and properties of aluminium-bearing high boron high speed steel

Heat treatment is of great significance to the performance improvement of high speed steel. Via heat treatment, the microstructure of high speed steel can be improved, thus greatly improving the material performance. The effect of tempering temperature on the microstructure of aluminium-bearing high boron high speed steel (AB-HSS) was investigated by optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The hardness and wear resistance of the alloy at different tempering temperatures were tested by Rockwell hardness tester, micro-hardness tester and wear tester. The experimental results indicate that the tempering microstructure of aluminium-bearing high boron high speed steel consists of α-Fe, M₂B and a few of M₂₃(C, B)₆. Tempering temperature could greatly affect the wear resistance of materials. With the increase of tempering temperature, the wear resistance of aluminium-bearing high boron high speed steel firstly increase and then decrease. The alloy tempered at 450 °C has the best wear resistance and minimum wear weight loss. This study provides a reference for the formulation of heat treatment process of aluminium-bearing high boron high speed steel.