The effect of high temperature annealing in different atmospheres on microstructure of ODS materials

Mechanically alloyed oxide dispersion strengthened materials MA 6000 and MA 956 have been annealed at 1100ºC for 24 and 240 hours in air, vacuum of 10 -3 Pa and hydrogen atmosphere.. Mass changes due to oxidation and evaporation were measured. Fracture surfaces, microstructure of the materials and changes in chemical composition were examined along with surface layers  evolution and pores formation. On fracture surfaces and polished sections, formation of voids and altered microstructure sub-surface zones in both materials has been studied. Different mechanisms causing void formation are discussed and proposed in discussion. Also the mechanisms and reaction sequences of surface oxidation reactions are examined

Residual life of external steel constructions

The contribution is focused to the aspects of prevention untimely damage of exterior steel constructions at variable climatic conditions. The aspects for assurance of continual service of strategic steel constructions (bridges, pipelines, pylons, pressure vessels, containers, frameworks, cranes, chimneys, towers, etc.) is by action of severe climatic conditions in our climatic zones deteriorative. The service safety of construction mentioned is decreasing and could cause preterm damages. To avoid preterm damage there are two ways. First is to create conditions excluding the damage and second is proposal of construction safety also after expected limit state. During the lifetime is needed to assure failure free service of external steel constructions stressed by variable loading. At the same time is needed to calculate with action of aggressiveness of external environment as well as worsen atmospheric conditions. From load and conditions analysis could be calculated the residual life of external steel constructions

Fracture toughness transition of ferritic-pearlitic steel at static and dynamic loading evaluated by Master curve concept

The paper focuses on assessing the usability of fatigue pre-cracked Charpy type specimens when evaluating the resistance of steel with ferritic-pearlitic structure to the initiation of unstable fractures. The suitability of using the specimens is evaluated on the basis of comparing experimentally established values of fracture toughness on pre-cracked Charpy type specimens and the values of this characteristics determined using Compact Tension (CT) specimens. For the evaluation and comparison of the fracture toughness temperature dependences determined on individual specimen types the master curve concept quantifying fracture toughness transition was applied. In the case of the steel employed, very good agreement was found to exist between the characteristics determined on individual types of specimen. It was shown that fracture toughness determined on pre-cracked Charpy type specimens can be regarded as a representative measure of resistance of the material employed to the brittle fracture occurrence

Surface property control by electron beam deflection during hardening

The usage of the high-energy electron beam source enables repeated surface quenching of chosen locations of an engineering part surface. Different techniques of electron beam deflection allow creating hardened layers of different shapes, hardness levels and thicknesses. Experiments were carried out with 42CrMo4 (1.7225) steel. The deflection modes tested were one-point, 6-point, line, field, and meander. The influence of process speed and defocusing of the electron beam was also taken into account. The electron beam surface quenching resulted in a very fine martensitic microstructure with a hardness of over 700 HV0.5. The thickness of the hardened layers depends on the deflection mode and is affected directly (except field deflection) by process speed. The maximum hardened depth (NCHD) was 1.49 mm. Electron beam defocusing affects the width of the hardened track and can cause extension of the trace up to 40%. The hardness values continuously decrease from the surface to the material core

Mechanical properties of AlSi10Mg alloy processed by SLM

The paper deals with mechanical properties of AlSi10Mg aluminium alloy processed by the selective laser melting (SLM) technique. The influence of surface quality and building orientation of the samples on mechanical properties was evaluated. It was found that orientation of the samples had no effect on tensile properties (UTS, 0.2% proof stress) whereas surface quality had a significant effect. An 11% increase in ultimate tensile strength was found in the case of samples of lower surface roughness, and an increase of almost factor two in elongation at break was found for machined samples in comparison to as-built samples

EFFECTS OF CHEMICAL COMPOSITION ON MECHANICAL PROPERTIES OF Al-Mg-Si-Mn BASED ALLOYS

Effects of chemical composition and heat treatment on the microstructural and mechanical properties of cast Al-Mg-Si-Mn alloys were investigated. The as-cast and heat treated alloys were investigated by microhardness, macrohardness and tensile stress measurements, scanning and transmission electron microscopy, energy dispersive X-ray analysis and differential scanning calorimetry. It was observed that the mechanical properties depend strongly on composition and addition of excess elements and eutectic phase. Heat treatment leads to the enhancement of all mechanical properties of alloys, which are the result of several mechanisms

EVALUATION OF WEAR BEHAVIOR OF Al-Si ALLOY USING SiC AS THE REINFORCEMENT

The current study investigates the wear behavior of the SiC particles reinforced Al-Si alloy composites developed using the stir casting process. The results were obtained from the wear tests of the cast Al-Si alloy and prepared SiC reinforcement composites containing 3 % wt and 9 % wt using fine and coarse size SiC particles. The wear test of all the developed composites were done at different testing conditions with varying loads. The analysis of wear traces, as well as the wear debris, was done at every composition but at higher loads. It was observed that the wear resistance was improved with increasing the amount as well as decreasing the size of the SiC particles. However, the wear rate of the composites increases with increasing the applied load. From the microstructural study of specimen after the wear test one can conclude that both adhesive and abrasive wear mechanisms contribute for wear of SiC particle composites

ZnO THIN FILMS PREPARED BY ATOMIC LAYER DEPOSITION

The purpose of this paper is present the influence of deposition conditions of nanometric zinc oxide thin films using atomic layer deposition on the mechanical and optical properties. The influence of the deposition temperature and the number of cycles on the transparency and adhesion of the ZnO, thin films was investigated. In addition, the results of chemical and phase composition analysis of the layers and their topography and structure were discussed. As a substrate for the investigated thin films was used glass. For the preparation of ZnO thin films was used ALD method. Selecting this method is justified by the high quality and good properties of the deposited layers

OPTIMIZATION OF CAPILLARY ACTION & BRASS CONSUMPTION IN DIP-BRAZING OF ROADSTER BICYCLE FRAMES

This paper describes the requirements of joint clearance between the mating parts, of lugged bicycle frame head, to be brazed by flow of molten filler material (brass) between the micro gap due to capillary action. Tolerance analysis was done to establish the practical requirements of clearances essential to facilitate the assembly of the bicycle frame tubes and mating head lugs. Consumption of brass was computed, by weight measurements, after dip brazing of the lugged joints. Excessive joint clearance between the mating parts was reduced, by cold compaction of the assembled joint on mechanical power press using a press tool. The compacted joints were dip brazed by dipping it partially in the molten brass. Comparison of tensile strength of the brazed joints was done with respect to the strength of parent steel tubes. Brazed samples were sectioned to confirm the flow of brass all along the length of the lugs with improved capillary action. Thickness of the micro layer of the brass between the lug bore and tube outer surface was measured on optical microscope. Reduction in brass consumption due to reduced clearance was estimated volumetrically between the contact area between the lugs and the tubes

Mechanical Properties of Stellite-6 coated AISI 316L Stainless Steel

Present paper describes the mechanical properties of Stellite-6 coated AISI 316 L stainless steel. Specimens were coated using Detonation Gun thermal spray process, with different coating thicknesses of Stellite-6 ranging from 50 µm to 150 µm. Afterwards their properties like tensile strength, impact strength and micro hardness were evaluated on the basis of the results obtained from the experimentation. For comparison of substrate and coated material the graphs were plotted. The coated specimens exhibited superior impact strength and microhardness than that of the bare specimens, whereas the tensile strength of coated specimens decreased marginally with the increase in coating thickness