The influences of multiscale-sized second-phase particles on fracture behaviour of overaged 7000 alloys

To identify the most important parameters of multiscale microstructural features influencing the fracture modes and resistance to damage, detailed microstructural and fractographic analysis of overaged 7000 alloy plates are performed using the broken plane-strain fracture toughness, K-Ic, test specimens. The geometric characteristics of differently sized second-phase particles are changed by the compositional variations. It was found that the fracture process involves three main micromechanisms. The dominant fracture mode changes with alloy purity, leading to fracture toughness degradation. Quantitative description of fractures by profilometry confirmed that crack initiation and propagation is fostered by the coarse Fe- and Si-rich particles. (C) 2009 Elsevier B. V. All rights reservedMesomechanics 2009 Conference, Jun 24-26, 2009, Oxford, Englan

Failure analysis of jet engine turbine blade

Jet engine turbine blade cast by investment precision casting of Ni-base superalloy, which failed during exploatation, was the subject of investigation. Failure analysis was executed applying optical microscopy (OM), transmission electron microscopy (TEM) using replica technique, scaning electron microscopy (SEM) and stress rupture life tests. On the ground of obtained results it was concluded that the failure occurred as a result of structural changes caused by turbine blade overheating above the exploitation temperature

Fractographic analysis of the aluminum matrix composite prepared by accumulative roll bonding

Recent research in the material science field is focused on the easy-to-apply and cost-effective production of the structural components with enhanced mechanical properties. As an answer to these new trends in the present study, the inexpensive household aluminum foils are used to produce the multilayer aluminum matrix composite. The aluminum matrix composites are manufactured by hot-rolling of the sandwiched foils and afterward subjected to microstructural characterization and mechanical testing. Analysis of the produced composite microstructure and fracture surface obtained after tensile testing was performed using the scanning electron microscopy (SEM). The qualitative fractographic analysis revealed that the ductile fracture features prevail in the overall fracture mode of the investigated multilayer composite, while the quantitative fractographic investigation allowed more detailed insight into the composite failure process and depicted critical parameters that led to the composite failure

Kinetika ciklične oksidacije titan aluminida

Automotive and aviation industries, as well as space-exploration technologies, are in demand for lightweight construction parts that are highly resistant to failure and degradation at elevated temperatures. Titanium aluminides are recognized as potential candidates for these applications since their low-density characteristics combined with good mechanical properties at elevated temperatures can fulfill the strict exploitation demands. Nevertheless, the resistance of titanium aluminides to high-temperature gas degradation should be additionally improved to enhance the performance of these materials in harsh working conditions. The scope of the present research was therefore directed to the investigation of Ti3Al-based alloy oxidation kinetics during the cyclic annealing at 600 oC and 900 oC in the air atmosphere to simulate exploitation conditions. Timedependent mass gain measurements were conducted for 120 h to obtain the kinetic models. The influence of the alloy's microstructural characteristics on its oxidative behavior was investigated with particular interest and for that purpose the examined Ti3Al-based alloy was subjected to different thermomechanical processing treatments prior to the high-temperature cyclic testing. Microscopic and X-ray diffraction methods were used to monitor the examined alloy characteristics before and after the oxidation tests. Obtained results indicated that an increase in the β phase fraction in the initial alloy microstructure influenced an increase in the alloy oxidation resistance, while an increase in the annealing temperature resulted in acceleration of the oxidative process.Strogi zahtevi automobilske i avio industrije, kao i kosmonautike, usmereni su na upotrebu lakih konstrukcionih delova visokootpornih prema otkazu i degradaciji na povišenim temperaturama. Titan aluminidi su zbog svoje male gustine i dobrih mehaničkih svojstava na povišenim temperaturama prepoznati kao materijali koji bi mogli ispuniti prethodno navedene stroge eksploatacione zahteve. Ipak, poboljšanje otpornosti titan aluminida prema visokotemperaturnoj degradaciji nameće se kao dodatni zahtev kako bi se poboljšao sveukupni odgovor ovih materijala na oštre eksploatacione uslove. Istraživanje je zato bio usmereno na ispitivanje kinetike oksidacije legure na bazi Ti3Al jedinjenja tokom cikljičnog žarenja na 600 oC i 900 oC na vazduhu, koje simulira uslove prisutne u toku eksploatacije. Kako bi se definisali kinetički modeli vršena su vremenski zavisna merenja prinosa mase u periodu od 120 h. Uticaj mikrostrukturnih karakteristika na oksidaciono ponašanje legure na bazi Ti3Al jedinjenja je posebno razmatran zbog čega je legura podvrgnuta različitim režimima termomehaničke prerade pre visokotemperaturnog cikličnog ispitivanja. Mikroskopske i redgenostrukturne metode su primenjene kako bi se pratila svojstva ispitivane legure pre i nakon oksidacionog procesa. Ostvareni rezultati su pokazali da povećanje sadržaja β faze u početnoj mikrostrukturi legure uslovljava povećanje njene otpornosti prema oksidaciji dok povećanje temperature žarenja utiče na ubrzavanje samog oksidacionog procesa

Optical microscopy as a simple method for analysis of boiler tube failure

A severely damaged low carbon steel boiler tube was the object of this investigation. Detailed microstructural characterization was performed by optical microscopy, whereas scanning electron microscopy (SEM) was applied only in a few cases. Results show that a variety of microstructures was formed in the material of the damaged boiler tube during its exploitation. The failure of the tube is the result of very inhomogeneous overheating. The side of the boiler tube toward fire (F) was exposed to high overheating temperature, which in some locations was well above the A3 transformation temperature. The side toward boiler (BL) was subjected to lower temperatures, i.e. in the region mostly between A1 and A3 temperatures. Variations in temperatures and cooling rates, which resulted in microstructural inhomogeneity, are the main cause for the formation and multiplication of stresses leading to the rupture of the tube

Effect of Processing Parameters on Ti3Al-based Alloy High-Temperature Cyclic Oxidation Kinetics

Efficient exploitation of the industrial components at elevated temperatures and in aggressive environments is demanded in modern industrial production. The Ti3Al-based alloys are proposed as materials that can meet these demands since it is determined that improved high- temperature corrosion resistance of industrial construction materials is often more significant for industrial exploitation than the improvement of their mechanical properties. Therefore, the aim of the present research was to determine the effect of various parameters, i.e. initial microstructure and high-temperature processing conditions, on the cyclic oxidation kinetics of the Ti3Al-based alloy with the Ti-24Al-11Nb (at.%) composition. Cyclic oxidation tests were conducted in air at 600 and 900 oC. The oxidation process was monitored up to 120 h by recording mass gain data as a function of time to define the kinetic models. Examination of alloy microstructure and alloy degradation during the cyclic oxidation was undertaken using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Alloy hot-rolled at 1050 oC and hot-rolled alloy subsequently thermally treated at 1200 oC were examined before and after cyclic high-temperature oxidation. Obtained results indicated that the initial alloy microstructure has a significant influence on its high-temperature oxidation behavior. Namely, hot-rolled alloy thermally treated at 1200 oC with a higher volume fraction of the β phase in the microstructure shows improved oxidation resistance compared to the alloy only hot-rolled at 1050 oC. An increase in oxidation temperature caused the progress in alloy degradation. In contrast to the compact external layer formed at the alloy surface after cyclic oxidation at 600 oC, during cyclic oxidation at 900 oC formation of a multi-layer scale was observed. The main products of oxidation are Al2O3 and TiO2. Kinetic models of the Ti-24Al-11Nb (at.%) alloy cyclic oxidation at 600 oC and 900 oC in the air are defined with linear and parabolic oxidation curves for most of the examined conditions

Tensile properties and fracture mechanism of IN-100 superalloy in high temperature range

Tensile properties and fracture mechanism of a polycrystalline IN-100 superalloy have been investigated in the range from room temperature to 900 °C. Optical microscopy (OM) and transmission electron microscopy (TEM) applying replica technique were used for microstructural investigation, whereas scanning electron microscopy (SEM) was utilized for fracture study. High temperature tensile tests were carried out in vacuumed chamber. Results show that strength increases up to 700 °C, and then sharply decreases with further increase in temperature. Elongation increases very slowly (6-7.5%) till 500 °C, then decreases to 4.5% at 900 °C. Change in elongation may be ascribed to a change of fracture mechanism. Appearance of a great number of microvoids prevails up to 500 °C resulting in a slow increase of elongation, whereas above this temperature elongation decrease is correlated with intergranular crystallographic fracture and fracture of carbides

Analysis of metal ion release from biomedical implants

Metallic biomaterials are commonly used for fixation or replacement of damaged bones in the human body due to their good combination of mechanical properties. The disadvantage of metals as implant materials is their susceptibility to corrosion and metal ion release, which can cause serious health problems. In certain concentrations metals and metal ions are toxic and their presence can cause diverse inflammatory reactions, genetic mutations or even cancer. In this paper, different approaches to metal ion release examination, from biometallic materials sample preparation to research results interpretation, will be presented. An overview of the analytical techniques, used for determination of the type and concentration of released ions from implants in simulated biofluids, is also given in the paper

Effect of recasting on the structure and properties of commercial Ni-Cr dental alloy

The Ni-Cr dental alloys are among the oldest restorative materials used in dentistry. Reuse of previously melted and cast dental alloys is a routine procedure used in dental laboratories to reduce the cost of dental restorations. Continuous reuse of the commercial Ni-Cr dental alloys, such as Wirron 99, can change numerous properties of these materials, and therefore the present study was aimed to establish the outcome of several recasting cycles on the Wirron 99 alloy properties. Obtained results reveal that alloy recasting resulted in the appearance of typical dendritic microstructures where the chemical composition of dendritic and interdendritic regions differs. Moreover, the results of the present study showed that the number of recasting cycles has a significant effect on the alloy microstructure, structure, electrical conductivity, and hardnes

Copper alloys with improved properties: standard ingot metallurgy vs. powder metallurgy

Three copper-based alloys: two composites reinforced with Al2O3 particles and processed through powder metallurgy (P/M) route, i.e. by internal oxidation (Cu-2.5Al composite) and by mechanical alloying (Cu-4.7Al2O3 ) and Cu-0.4Cr-0.08Zr alloy produced by ingot metallurgy (vacuum melting and casting) were the object of this investigation. Light microscope and scanning electron microscope (SEM) equipped with electron X-ray spectrometer (EDS) were used for microstructural characterization. Microhardness and electrical conductivity were also measured. Compared to composite materials, Cu-0.4Cr-0.08Zr alloy possesses highest electrical conductivity in the range from 20 to 800 ℃, whereas the lowest conductivity shows composite Cu-2.5Al processed by internal oxidation. In spite to somewhat lower electrical conductivity (probably due to inadequate density), Cu-2.5Al composite exhibits thermal stability enabling its application at much higher temperatures than materials processed by mechanical alloying or by vacuum melting and casting. http://dx.doi.org/10.5937/metmateng1403207