Thermomechanical Formulation of Freezing Point Depression Behavior of Liquid on Solid Surface With Nanostructure

In this study, we investigated the freezing point depression of liquids in nanostructures using a new thermomechanical method. First, we experimentally determined the freezing points of water, cyclohexane, and a certain organic material (Chem.A) in nanoscale structures using DSC measurements. Thereafter, we formulated a new equation by improving the Gibbs–Thomson equation, which is the conventional formula for representing the freezing point depression of a liquid in nanostructures. We introduced a new term in this new equation to represent the increase in the kinetic energy of the liquid molecule as a result of collision between the liquid molecules and nanostructure walls. Subsequently, we evaluated the solid–liquid interface free energy of sublimation materials by fitting the theoretical freezing point derived from the new equation to experimental data. In this study, we succeeded in reproducing the experimental data of freezing point depression using the proposed equation. In particular, the freezing points of cyclohexane and Chem.A in the nanostructure were better fitted by this new equation at 10 nm or more compared with the conventional equation. Our results show that the interaction between the wall of the nanostructure and liquid molecules affects freezing point depression.

CHANGES IN PIPE GEOMETRY DURING SEQUENTIAL CREATION OF STRESSES ON THE INNER SURFACE UNDER EXTERNAL THERMOMECHANICAL EFFECTS

In modern high-tech industry, flexible pipe technology is widely used. Pipe benders are an integral part of pipeline systems. The most widely used are methods of pipes cold bending, which are accompanied by a number of negative phenomena – such as reduction in the crackle of the wall on outer side of the bend, ovalization of the cross section and formation of bumps. The article presents a study of influence of deformation technology of pipe billets by rolling with high tension on the structure and properties of the billet’s material. The method of pipe deformation by rolling with tension allows obtaining radial bending of the billet without its destruction and without causing obvious defects of the surface and microstructure. The tests were carried out on the samples from steel of 3sp and 12Kh18N10T grades. Research of the microstructure was performed in accordance with GOST 5639 – 82, of mechanical properties – with GOST 1397 – 84, of microhardness – with GOST 9450 – 76. The article examines the effect of changes in geometry of the pipe billet on its structure and properties. The process of pipe deformation by rolling leads to changes in the mechanical properties of the tested materials. The values of micro hardness and strength increase, while the grain points decrease. In the process of deformation, it is possible to change the microstructure of the material as a result of structural transformations (quenching). In the thermomechanical method of deformation, plastic flow of metal suggests possible change in structure of pipe walls as a result of recrystallization and heat treatment of material of the bend area. Therefore, it requires further study and more in-depth analysis of this technology.

Pengaruh Persentase Reduksi Warm Rolling Terhadap Sifat Mekanik Paduan Cu-Zn 70/30

Warm rolling is one of the thermomechanical method has several advantages such as produces high mechanical properties, but does not decrease % elongation and toughness value because partial recrystallization phenomenon that produces micron-sized new grain. This paper reports the results of an investigation carried out on the effects of holding time annealing to mechanical properties Cu-Zn 70/30 alloy. These alloy after homogenization process and quenched in the air then heated to temperature of 300°C, later the heated copper samples are warm rolled at 25%, 30%, and 35% reduction, after that heated at temperature 300°C and held during 120 minutes. Then sample is experienced rewarm rolling with reduction 25%, 30%, and 35%. The results obtained showed that the ultimate tensile strength and yield strength are higher proportional with the increasing of % reduction, their values are 501,1 MPa; 599,3 MPa; later decrease to 546, 5 MPa and to yield strength are 441,8 MPa; 466,1 MPa; then decrease to 458,6 MPa. Moreover hardness value increase proportional with % reduction such as 154 HV; 162 HV; after that decrease to 160 HV While, % elongation decreases inversely proportional with % reduction namely 12,4%; 8,2%; later increase to 11,2 %. It is caused of the partial recrystallization phenomenon as evidenced by the presence micron-sized. Warm rolling merupakan salah satu metode termomekanik yang mempunyai beberapa keuntungan yaitu salah satunya menghasilkan sifat mekanik yang tinggi, namun tidak mengurunkan nilai keuletan karena adanya fenomena rekristalisasi parsial yang menghasilkan butiran baru berbentuk micron. Paper ini menjelaskan tentang hasil penelitian berupa pengaruh persentase reduksi terhadap sifat mekanis paduan Cu-Zn 70/30. Paduan Cu-Zn 70/30 setelah dilakukan proses homogenisasi dan didinginkan di udara lalu dipanaskan ke suhu 300°C, kemudian masing-masing dilakukan warm rolling dengan persentase reduksi sebesar 25%, 30%, dan 35% kemudian ditahan di suhu 300°C dalam waktu 120 menit. Selanjutnya sampel dilakukan rewarm rolling dengan persentase reduksi sebesar 25%, 30%, dan 35%. Hasil penelitian yang dilakukan antara lain nilai kekuatan tarik (UTS dan YS) yang semakin tinggi sebanding dengan peningkatan % reduksi warm rolling yaitu masing-masing untuk nilai UTS sebesar 501,1 MPa; 599,3 MPa; lalu menurun menjadi 546,5 MPa serta untuk nilai kekuatan luluh sebesar 441,8 MPa; 466,1 MPa; lalu menurun menjadi 458,6 MPa. Selain itu, nilai kekerasan meningkat sebanding dengan peningkatan % reduksi warm rolling masing-masing sebesar 154 HV; 162 HV; lalu menurun menjadi 160 HV. Sedangkan persentase elongasi semakin menurun berbanding terbalik dengan peningkatan % reduksi masing-masing sebesar 12,4%; 8,2%; lalu meningkat menjadi 11,2%. Hal tersebut disebabkan karena adanya fenomena rekristalisasi parsial yang dibuktikan dengan kehadiran butir kecil berukuran mikron. Keywords:Cu-Zn 70/30 alloy, warm rolling, anneal, % reduction, mechanical properties