On the evaluation of stability of rare earth oxides as face coats for investment casting of titanium

Attempts have been made to evaluate the thermal stability of rare earth oxide face coats against liquid titanium. Determination of microhardness profiles and concentration profiles of oxygen and metallic constituents of oxide in investment cast titanium rods has allowed grActation of relative stability of rare earth oxides. The relative stability of evaluated oxides in the order of increasing stability follows the sequence CeO2 — ZrO2 — Gd2O3 — didymium oxide — Sm2O3 —Nd2O3 — Y2O3. The grading does not follow the free energy data of the formation of these oxides. A better correlation with the experimental observations is obtained when the solubility of the metallic species in titanium is also taken into consideration.

Influence of Die Surface Textures during Metal Forming-A Study Using Experiments and Simulation

Friction plays an important role in metal forming processes, and the surface texture of the die is a major factor that influences friction. In the present investigation, experiments were conducted to understand the role of surface texture of the harder die surface and load on coefficient of friction. The data analysis showed that the coefficient of friction is highly dependent on the surface texture of the die surface. Assigning different magnitude of coefficients of friction, obtained in the experiments, at different regions between the die and the workpiece, Finite element (FE) simulation of a compression test was carried out to understand the effect of friction on deformation and stress/strain-rate distribution. Simulation results revealed that, owing to the difference in coefficient of friction, there is a change in metal flow pattern. Both experimental and simulation results confirmed that the surface texture of the die surface and thus coefficient of friction directly affects the strain rate and flow pattern of the workpiece.

Casting and heat treatment variables of Al–7Si–Mg alloy

A review of the research work that has been carried out thus far relating the casting and heat treatment variables to the structure and mechanical properties of Al–7Si–Mg (wt-%) is presented here. Although specifications recommend a wide range of magnesium contents and a fairly high content of iron, a narrow range of magnesium contents, closer to either the upper or lower specified limits depending on the properties desired, and a low iron content will have to be maintained to obtain optimum and consistent mechanical properties. A few studies have revealed that the modification of eutectic silicon slightly increases ductility and fracture toughness and also that the effect of modification is predominant at low iron content. Generally, higher solidification rates give superior mechanical properties. Delayed aging (the time elapsed between quenching and artificial aging during precipitation hardening) severely affects the strength of the alloy. The mechanism of delayed aging can be explained on the basis of Pashley's kinetic model. It has been reported that certain trace additions (cadmium, indium, tin, etc.) neutralise the detrimental effect of delayed aging. In particular, it should be noted that delayed aging is not mentioned in any of the specifications. With reference to the mechanism by which trace additions neutralise the detrimental effect of delayed aging, various hypotheses have been postulated, of which impurity–vacancy interaction appears to be the most widely accepted.

"Die Barbaren werden von Russen gespielt" : Etniset hahmot Wladimir Kaminerin kertomuskokoelmissa "Russendisko" ja "Mein deutsches Dschungelbuch"

Pro gradu -tutkielmassani tarkastelen hahmojen etnisyyttä Wladimir Kaminerin kahdessa kertomuskokoelmassa. Kaminerin, saksalaistuneen venäjänjuutalaisen, esikoisteos Russendisko kuvaa kertojan kotiutumista itäiseen Berliiniin sekä värikästä arkea monikulttuurisessa pääkaupungissa. Mein deutsches Dschungelbuchissa Kaminer matkustaa ympäri Saksaa esittämässä tekstejään ja kirjoittaa havainnoistaan kirjaa. Vitsikkään tyylin lisäksi kokoelmien kertomuksia yhdistävänä tekijänä toimii autobiografisia piirteitä omaava kertojahahmo, yleensä nimettyjä etnisyyksiä edustavien ja ohueksi jäävien sivuhenkilöiden tullessa ja mennessä. Näistä piirteistä nousevat tutkielmani kaksi näkökulmaa etnisyyteen: tutkin, miten etnisyys suhteutuu ensinnäkin kertojahahmoon ja toiseksi eri ihmisryhmien stereotyyppiseen esittämiseen. Tutkielmani lähtökohtana on käsitys etnisyydestä – kuulumisesta johonkin kansaan tai heimoon – luonnollisen sijasta kulttuurisesti konstruoituna ilmiönä. Kertojahahmon etnisyyden tutkimisessa hyödynnän hybridin käsitettä, jolla viitataan selvärajaisten etnisyyksien sijaan niiden sekoittumiseen. Kertojahahmon juutalaisuus paljastuu useiden diskurssien jännitteiseksi risteyspaikaksi: kertojahahmo vastustaa pyrkimyksiä kiinnittää itseään uskonnollisesti ja kulttuurisesti rajattuun etniseen kompleksiin, mutta yhdistyy kaupunkielämästä inspiraationsa löytävänä individualistisena intellektuellina urbaanin juutalaiskirjallisuuden traditioon. Kertojahahmon etnisyyden ulottuvuuksista korostuu teksteissä selkeimmin venäläisyys, joka osoittautuu tietoisen performatiiviseksi ja saksalaisille suunnatuksi. Kielellisesti assimiloituneen mutta venäläisenä esiintyvän kertojahahmon asema useampien etnisyyksien kartoittamattomassa välitilassa avaa mahdollisuuden pinttyneiden etnisten vastakkainasetteluiden kritiikille. Kertojahahmo sijoittaa itsensä intertekstuaaliseen tilaan tavalla, joka kyseenalaistaa korkeakulttuuristen kaanonien lisäksi ajatuksen puhtaista kansallisista kirjallisuuksista. Relevantiksi kehykseksi Kaminerin tekstien tulkinnassa osoittautuukin transeurooppalainen pikareski-genre, jonka veijarisankareita naiivin ulkopuolisuutensa satiirin palvelukseen valjastava kertojahahmo läheisesti muistuttaa. Kertojahahmon hybridi etnisyys on yhteydessä myös siihen, miten tekstien oletetaan esittävän ja edustavan erilaisia ihmisryhmiä: se mahdollistaa hankalienkin teemojen häpeilemättömän käsittelyn. Etnisiä stereotypioita – etnistä ryhmää koskevia pinttyneitä representaatioita, joihin ihmiset turvautuvat pyrkiessään selittämään tai hallitsemaan toisia – tarkastelen imagologian ja kriittisen kulttuurintutkimuksen välinein. Etniset stereotypiat ovatkin keskeisiä Kaminerin rakentaessa lukuisia sivuhenkilöitään, jotka pelkistyvät useimmiten litteiksi, jopa karikatyyrinomaisiksi etnisyyksiensä edustajiksi. Kaminerin tekstit kiertyvät kuitenkin myös samaisten etnisten stereotypioiden satiiriksi. Yhtäältä ironian kohteena on stereotyypittelyn prosessi, jossa toisen määrittely essentialistisin termein ja yleistyksien kautta johtaa absurdeihinkin virhetulkintoihin. Toisaalta kertojahahmon toteava kuvailutapa paljastaa etnisten stereotypioiden haitalliset yhteiskunnalliset vaikutukset. Kaminerin satiirin terä kohdistuu kantasaksalaisiin, jotka näkevät muut etnisyydet pitkälti omia tarpeitaan, pelkojaan ja fantasioitaan palvelevien stereotypioiden kautta. Tutkielmani kuitenkin osoittaa, että maahanmuuttajataustaiset henkilöhahmot kykenevät myös tuotteistamaan etnisiä stereotypioita – toki ahtaissa, yhteiskunnallisten valtarakenteiden määrittämissä rajoissa. Olennaista on etnisiin stereotypioihin sisältyvä kaksiteräisyys: sama ennakko-oletusten kimppu saatetaan yhteydestä riippuen esittää ja tulkita joko negatiiviseksi tai positiiviseksi. Kaminerin tekstit tarjoavat huumorin kautta luvallisen kanavan käsitellä ja purkaa etnisyyden akseleilla liikkuvia odotuksia, pelkoja ja aggressioita, jotka ovat pitkään olleet lähes tabuja saksalaisessa yhteiskunnassa. Samalla Kaminerin tekstit puhuvat sellaisen maailman puolesta, jossa etnisyys pikemminkin mahdollistaisi kuin sitoisi inhimillistä vuorovaikutusta.

Water Modeling Study Of The Jet Characteristics In A Continuous-Casting Mold

The jet characteristics and the fluid flow pattern in a continuous slab caster have been studied using a water model. The fluid jet is studied under free fall and submerged discharge conditions. In the latter case, the jet was followed by dye-injection technique and image analyser was used to find out the effect of nozzle parameters on jet-spread angle, jet-discharge angle and the volume entrainment by the jet. All free-fall jets with nozzle port angle zero and upward are found to be spinning. Some of the free-fall jets with downward nozzle-port angle are found to be spinning and rest are smooth. The spinning direction of the jets are found to change with time. The well depth, port diameter and the inner diameter of the nozzle have a clear effect on the free-fall jets with downward port angle. The jet-spread angle is found to be about 17-degrees for smooth jets. The spread angle for spinning jet increases as the nozzle-port angle is increased from downward 25 to upward 15-degrees. The jet-discharge angle is always downward even when the nozzle-discharge ports are angled upward. The extent of volume entrainment by the spinning jet is higher and it increases as the nozzle-port angle is increased from 25 downward to 15-degrees upward.

Control of transient thermal response during sequential open-die forging: A trajectory optimization approach

A trajectory optimization approach is applied to the design of a sequence of open-die forging operations in order to control the transient thermal response of a large titanium alloy billet. The amount of time tire billet is soaked in furnace prior to each successive forging operation is optimized to minimize the total process time while simultaneously satisfying constraints on the maximum and minimum values of the billet's temperature distribution to avoid microstructural defects during forging. The results indicate that a "differential" heating profile is the most effective at meeting these design goals.

Microstructural evolution in liquid metal processed Al-alloy/SiCp composites

Al-Zn-Mg/SiCP composites processed by a liquid metal processing (stir casting) technique have been microstructurally characterised in the as-cast and extruded conditions. Uniform distribution of SiCP is observed with few defects, such as particle clusters, which are due to partial wetting and associated gas porosity. The constituent particles are associated with SiCP although their composition remains unaffected compared with the control alloy. Hot extrusion of the composite using a shear type die showed banding of particles in the extruded direction with 9 vol.% composite. Such defects however, are not predominant in 18% SiCP extruded composites. The presence Of Mg2Si is detected at the particle matrix interface as well as in the matrix.

Casting of titanium and titanium alloys

Titaniuni and its alloys have many applications in aerospace, marine and other engineering industries. Titanium requires special melting techniques because of its high reactivity at elevated temperatures and needs special mould materials and methods for castings. This paper reviews the development of titanium casting technology.

Evaluation of the reactivity of titanium with mould materials during casting

A methodology for evaluating the reactivity of titanium with mould materials during casting has been developed. Microhardness profiles and analysis of oxygen contamination have provided an index for evaluation of the reactivity of titanium. Microhardness profile delineates two distinct regions, one of which is characterised by a low value of hardness which is invariant with distance. The reaction products are uniformly distributed in the metal in this region. The second is characterised by a sharp decrease in microhardness with distance from the metal-mould interface. It represents a diffusion zone for solutes that dissolve into titanium from the mould. The qualitative profiles for contaminants determined by scanning electron probe microanalyser and secondary ion mass spectroscopy in the as-cast titanium were found to be similar to that of microhardness, implying that microhardness can be considered as an index of the contamination resulting from metal-mould reaction.

Metal mould reactions during casting of titanium in zircon sand moulds

Metal-mold reaction during Ti casting in zircon sand molds has been studied using scanning electron microscope, energy and wave length dispersive analysis of X-rays, X-ray diffraction, microhardness measurements, and chemical analysis. Experimental results suggest that oxides from the mold are not fully leached out by liquid Ti, but oxygen is preferentially transferred to liquid Ti, leaving behind metallic constituents in the mold as lower oxides or intermetallics of Ti. The electron microprobe analysis has revealed the depth profile of contaminants from the mold into the cast Ti metal. The elements Si, Zr and O were found to have diffused to a considerable distance within the Ti metals. A possible mechanism has now been evolved in regard to the reactions that occur during casting of Ti in zircon sand molds.

Effect of pouring temperature on cooling slope casting of semi-solid Al-Si-Mg alloy

Present trend of semi-solid processing is directed towards rheocasting route which allows manufacturing of near-net-shape cast components directly from the prepared semi-solid slurry. Generation of globular equi-axed grains during solidification of rheocast components, compared to the columnar dendritic structure of conventional casting routes, facilitates the manufacturing of components with improved mechanical properties and structural integrity. In the present investigation, a cooling slope has been designed and indigenously fabricated to produce semi solid slurry of Al-Si-Mg (A356) alloy and successively cast in a metallic mould. The scope of the present work discusses about development of a numerical model to simulate the liquid metal flow through cooling slope using Eulerian two-phase flow approach and to investigate the effect of pouring temperature on cooling slope semi-solid slurry generation process. The two phases considered in the present model are liquid metal and air. Solid fraction evolution of the solidifying melt is tracked at different locations of the cooling slope, following Schiel's equation. The continuity equation, momentum equation and energy equation are solved considering thin wall boundary condition approach. During solidification of the liquid metal, a modified temperature recovery scheme has been employed taking care of the latent heat release and change of fraction of liquid. The results obtained from simulations are compared with experimental findings and good agreement has been found.

A high precision instrument to measure angular and binocular deviation introduced by aircraft windscreens by using a shadow casting technique

Objects viewed through transparent sheets with residual non-parallelism and irregularity appear shifted and distorted. This distortion is measured in terms of angular and binocular deviation of an object viewed through the transparent sheet. The angular and binocular deviations introduced are particularly important in the context of aircraft windscreens and canopies as they can interfere with decision making of pilots especially while landing, leading to accidents. In this work, we have developed an instrument to measure both the angular and binocular deviations introduced by transparent sheets. This instrument is especially useful in the qualification of aircraft windscreens and canopies. It measures the deviation in the geometrical shadow cast by a periodic dot pattern trans-illuminated by the distorted light beam from the transparent test specimen compared to the reference pattern. Accurate quantification of the shift in the pattern is obtained by cross-correlating the reference shadow pattern with the specimen shadow pattern and measuring the location of the correlation peak. The developed instrument is handy to use and computes both angular and binocular deviation with an accuracy of less than +/- 0.1 mrad (approximate to 0.036 mrad) and has an excellent repeatability with an error of less than 2%. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4769756]