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

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

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

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

The role of ain precipitates in the development of a strong (111) texture on subsequent cold rolling and annealing of Al-stabilized steel

The thermomechanical treatment consisting of either static (SSA) or dynamic strain aging (DSA) followed by cold rolling and annealing was applied to develop a strong texture in Al-stabilized steel. The effectiveness of SSA and DSA treatments in developing a high average plastic strain ratio and a high (222)/(200) intensity ratio is related to the size and distribution of AlN precipitates. It is assumed that a fine distribution of AlN particles, capable of pinning effectively subgrain boundaries produced on subsequent cold rolling and annealing, is essential for developing of a high proportion of recrystallized grains with the (222) orientation at the expense of grains with the (200) orientation

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

The effects of microalloying with silicon and germanium on microstructure and hardness of a commercial aluminum alloy

The effect of small additions of Si and Ge on the microstructure and hardness was investigated during aging of a commercial 2219 aluminum alloy It was found that for the same level of microalloying in alloy 2219SG (containing St and Ge), a maximum hardness was achieved 3 times faster than in alloy 2219S (without Ge). The accelerated precipitation kinetics is a consequence of the presence of fine Si-Ge particles. serving as heterogeneous precipitation sites for theta strengthening particles

The effect of an Ni-Cr protective layer on cyclic oxidation of Ti3Al

The effect of an 80Ni-20Cr (at.%) metallic coating on the cyclic oxidation behaviour of a Ti3Al-based alloy with the composition Ti-25Al-11Nb (at.%) was investigated in this study. Cyclic oxidation tests were carried out in air at 600 degrees C and 900 degrees C for 120 h. For one cycle test, the specimens were held for 24 h at test temperature and then furnace-cooled to room temperature. The oxidation rate was determined by plotting the mass gain per unit surface area of the specimen vs. exposure time. The morphology and composition of the oxidation products were characterized on the cross-section of the specimens by scanning electron microscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy. The oxidation scale forms during exposure at both 600 degrees C and 900 degrees C. TiO2 is the main oxide component, whereas the Al2O3 layer appears only discontinuously. The remarkable improvement in oxidation resistance at 900 degrees C was attributed to the chemical composition and structure of the scale formed on the 80Ni-20Cr coating