Combinatorial measurement of critical cooling rates in aluminum-base metallic glass forming alloys

Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability. We use this method to identify glass forming alloys and study the composition effect on the critical cooling rate in the Al–Ni–Ge system where we identified Al51Ge35Ni14 as the best glass forming composition with a critical cooling rate of 104 K/s.

FRAKSINASI KERING MINYAK KELAPA MENGGUNAKAN KRISTALISATOR SKALA 120 KG UNTUK MENGHASILKAN FRAKSI MINYAK KAYA TRIASILGLISER0L RANTAI MENENGAH

<p>ABSTRAK<br />Minyak kelapa merupakan sumber medium chain triglycerides<br />(MCT) utama. Melalui proses fraksinasi dapat dihasilkan fraksi minyak<br />dengan kandungan MCT tinggi. Penelitian ini bertujuan untuk mempelajari<br />pengaruh berbagai faktor perlakuan dingin terhadap kristalisasi dan<br />fraksinasi minyak kelapa, serta untuk menetapkan prosedur pendinginan<br />yang efektif dalam menghasilkan fraksi minyak dengan kandungan MCT<br />tinggi. Penelitian dilaksanakan di Laboratorium SEAFAST CENTER IPB<br />dari bulan Maret 2012 sampai bulan Februari 2013. Fraksinasi dilakukan<br />dengan memanaskan minyak pada suhu 70°C lalu didinginkan pada<br />berbagai laju pendinginan untuk mencapai beberapa variasi suhu<br />kristalisasi, diaduk dengan kecepatan 15 rpm, dibiarkan mengkristal pada<br />lama waktu yang berbeda (hingga 900 menit), serta difraksinasi dengan<br />penyaringan vakum menggunakan kertas Whatman 40. Tiga tahap<br />pendinginan yang merupakan faktor kunci keberhasilan proses kristalisasi<br />minyak kelapa yaitu tahap pendinginan awal dari suhu 70 hingga 29°C;<br />tahap pendinginan kritis 29°C hingga suhu kristalisasi; dan tahap<br />kristalisasi itu sendiri. Pada tahap pertama minyak kelapa didinginkan<br />secepat mungkin untuk menurunkan waktu proses, tetapi pada tahap kedua<br />harus dilaksanakan dengan laju pendinginan lambat (kurang dari 0,176°C/<br />menit) untuk menghasilkan kristal yang berukuran besar dan tidak mudah<br />meleleh. Minyak dengan kandungan triasilgliserol tinggi dapat diperoleh<br />dari fraksi olein minyak kelapa. Pada perlakuan suhu kristalisasi 21,30-<br />21,73°C untuk laju pendinginan kritis antara 0,013 hingga 0,176°C/menit,<br />semakin rendah laju pendinginan kritis dan semakin lama proses<br />kristalisasi maka kandungan MCT fraksi olein yang dihasilkan akan<br />semakin tinggi.<br />Kata kunci: minyak kelapa, laju pendinginan, kristalisasi, fraksinasi, MCT</p><p>ABSTRACT<br />Coconut oil is the main source of medium chain triglycerides<br />(MCT). Fractionation produce oil fraction containing MCT concentrate.<br />This research aims to study the influence of various factors of cooling<br />treatment on the crystallization and fractionation of coconut oil, and to<br />establish effective cooling procedure to produce oil fraction with high<br />MCT content. The research was conducted in Laboratorium of SEAFAST<br />CENTER IPB from March 2012 to February 2013. Coconut oil was<br />heated at 70°C then cooled at different cooling rate to reach various<br />crystalization temperatures. The oil was then stirred at 15 rpm and allow to<br />crystallized at different period of time (up to 900 min), and finally<br />fractionated by vacuum filtration using Whatman #40 paper. Fractionation<br />temperatures was the same as crystalization temperature. The results<br />showed that there were three distinct cooling regimes critical to<br />crystallization process, i.e temperature range from 70 to 29°C; 29°C to<br />crystallization temperature; and crystallization temperature. In the first<br />regime, melted coconut oil might be cooled quickly to save time, but in the<br />second regime need be done with a cooling rate of less than 0.176°C/min<br />to produce physically stable crystal. Oil with high triacylglycerol content<br />could be obtained from olein fraction of coconut oil. At the crystallization<br />temperature 21.30-21.73°C for the critical cooling rate between 0.013 to<br />0.176°C/min, the higher MCT content of olein fraction were produced by<br />the lower critical cooling rate and the longer crystallization process.<br />Keywords: fractionation, crystallization, MCT, coconut oil, cooling rate.</p>

Effect of Strain on Transformation Diagrams of 100Cr6 Steel

Based on dilatometric tests, the effect of various values of previous deformation on the kinetics of austenite transformations during the cooling of 100Cr6 steel has been studied. Dilatometric tests have been performed with the use of the optical dilatometric module of the plastometer Gleeble 3800. The obtained results were compared to metallographic analyses and hardness measurements HV30. Uniaxial compression deformations were chosen as follows: 0, 0.35, and 1; note that these are true (logarithmic) deformations. The highly important finding was the absence of bainite. In addition, it has been verified that with the increasing amount of deformation, there is a further shift in the pearlitic region to higher cooling rates. The previous deformation also affected the temperature martensite start, which decreased due to deformation. The deformation value of 1 also shifted the critical cooling rate required for martensite formation from the 12 °C/s to 25 °C/s.

Exploring the Phase Space of Multi-Principal-Element Alloys and Predicting the Formation of Bulk Metallic Glasses

Multi-principal-element alloys share a set of thermodynamic and structural parameters that, in their range of adopted values, correlate to the tendency of the alloys to assume a solid solution, whether as a crystalline or an amorphous phase. Based on empirical correlations, this work presents a computational method for the prediction of possible glass-forming compositions for a chosen alloys system as well as the calculation of their critical cooling rates. The obtained results compare well to experimental data for Pd-Ni-P, micro-alloyed Pd-Ni-P, Cu-Mg-Ca, and Cu-Zr-Ti. Furthermore, a random-number-generator-based algorithm is employed to explore glass-forming candidate alloys with a minimum critical cooling rate, reducing the number of datapoints necessary to find suitable glass-forming compositions. A comparison with experimental results for the quaternary Ti-Zr-Cu-Ni system shows a promising overlap of calculation and experiment, implying that it is a reasonable method to find candidates for glass-forming alloys with a sufficiently low critical cooling rate to allow the formation of bulk metallic glasses.

Development of Precipitation Hardening Parameters for High Strength Alloy AA 7068

The mechanical properties after age hardening heat treatment and the kinetics of related phase transformations of high strength AlZnMgCu alloy AA 7068 were investigated. The experimental work includes differential scanning calorimetry (DSC), differential fast scanning calorimetry (DFSC), sophisticated differential dilatometry (DIL), scanning electron microscopy (SEM), as well as hardness and tensile tests. For the kinetic analysis of quench induced precipitation by dilatometry new metrological methods and evaluation procedures were established. Using DSC, dissolution behaviour during heating to solution annealing temperature was investigated. These experiments allowed for identification of the appropriate temperature and duration for the solution heat treatment. Continuous cooling experiments in DSC, DFSC, and DIL determined the kinetics of quench induced precipitation. DSC and DIL revealed several overlapping precipitation reactions. The critical cooling rate for a complete supersaturation of the solid solution has been identified to be 600 to 800 K/s. At slightly subcritical cooling rates quench induced precipitation results in a direct hardening effect resulting in a technological critical cooling rate of about 100 K/s, i.e., the hardness after ageing reaches a saturation level for cooling rates faster than 100 K/s. Maximum yield strength of above 600 MPa and tensile strength of up to 650 MPa were attained.

Investigation of the Quench Sensitivity of an AlSi10Mg Alloy in Permanent Mold and High-Pressure Vacuum Die Castings

The quench sensitivities of an AlSi10Mg alloy in permanent mold (PM) and high-pressure vacuum die (HPVD) castings were investigated with time–temperature–transformation and time–temperature–property diagrams using an interrupted quench technique. The quench-sensitive temperature range of the HPVD casting sample is 275–450 °C, and its nose temperature is 375 °C. The quench-sensitive range of the PM casting sample is 255–430 °C, and the nose temperature is 350 °C. The mechanical strength versus the cooling rate in both casting samples were predicted via a quench factor analysis and verified experimentally. The critical cooling rate of the HPVD casting sample is 20 °C/s whereas it is 17 °C/s for the PM casting sample. With a shorter critical time, higher nose temperature, and higher critical cooling rate, the HPVD casting sample exhibits a higher quench sensitivity than the PM casting sample. The differences in the quench sensitivities of the AlSi10Mg alloy due to the different casting processes is explained via the different precipitation behavior. At the nose temperature, coarse β-Mg2Si precipitates mainly precipitate along the grain boundaries in the HPVD casting sample, whereas rod-like β-Mg2Si precipitates distribute in the aluminum matrix in the PM casting.