Dissertations for the scientific stage of the candidate of technical sciences for specialty 05.02.01 «Мaterials science» (13 – Mechanical engineering). – State Higher Educational Establishment "Pridniprovska State Academy of Civil Engineering and Architecture", Ministry of Education and Science of Ukraine, Dnipro, 2020.
The dissertation is based on the development of a scientifically-practical design, which has been rejected in the process of preparing a complex of powers in pipes from the titanium alloy Ti–3Al–2,5V, especially singing texture.
Essence of the scientific and applied problem, which is considered in the research paper consists in creating and implementing in practice theoretical and technological foundations of elaborating a process of production of titanium alloy tubes for responsible purposes, namely, aircraft building. In order to ensure high operational reliability, the tubes manufactured in Ukraine according to foreign standards ASM and ASTM are subject to requirements to their properties and texture. To ensure satisfaction of standard requirements, it is necessary to elaborate the manufacturing processes based on creation of certain types of crystallographic texture which affects mechanical and processing characteristics and provides specific strength in the process of working.
Practical significance of theoretical and technological developments consists in improvement of the process of production of titanium alloy tubes and bettering quality indicators of their operation.
The technology of making seamless tubes of titanium alloy of Ti–3Al–2,5V type continues to develop because this alloy is used in ever increasing number of production programs. Such progress dictates the need to expand studies aimed at improvement of manufacturing processes to achieve desired mechanical properties, structure and certain types of texture in the finished tube material determining its properties, fatigue resistance and deformability.
Creating a certain type of texture in the manufacture of titanium alloy tubes is a new challenge for the pipe and tube industry. It requires serious research efforts. This is also a very important problem for Ukrainian manufacturers of titanium alloy tubes. Moreover, it is necessary to combine creation of certain structure types, properties and textures as well as processing characteristics of titanium tubes.
Change and heredity of tube texture after pressing, cold working and heat treatment were traced. Texture in hot-extruded tubes was stable and changed slightly with subsequent cold working. To change the texture, it is necessary to change the cold rolling schedules.
The study of influence of large strain ratios and the factor Q (the wall to diameter strain ratio) showed the possibility of influencing the properties and texture of cold-worked tubes.
The contractive strain ratio (CSR) is an important indicator in the production of Ti–3Al–2,5V alloy tubes. In accordance with foreign standards, it characterizes the tube texture. Achieving it in the tube making process is a hard task.
The contractive strain ratio which is set at 1,3…3,5 in regulatory documents, does not always provide a necessary set of mechanical and especially processing properties. The optimal contractive strain ratio which characterizes texture in the manufacture of tubes is 1,5…2,5. At its higher values, a number of tubes do not withstand processing tests and also have a higher level of mechanical properties compared to the required ones.
Еditional special features of the formation of structure, mechanical and technological powers, as well as the texture of pipes at the stages of pressure, cold deformation, as well as different types of thermal treatment: recrystallization, overwhelming fires.
Practical value of the results obtained in the performed studies consists in that proposals for real industrial production of tubes of Ti–3Al–2,5V alloy (Grade 9) were elaborated and proposed based on them and their theoretical substantiation:
- parameters of hot deformation with high values of anisotropy properties in wall thickness of hot-worked tubes, namely, decrease in temperature and speed of the pressing process;
- achievement of high relative contractive strain ratio (1,3…2,5) which is ensured by creation of the radial texture component in tubes at a level of 60…70 %;
- optimal contractive strain ratio should be at a level of 1,3…2,5 to achieve the tube quality specified in standards;
- to create a predominantly radial texture, the ratio of wall thickness to diameter strain (coefficient Q) must be not less than 2,5…3;
- a technology was elaborated and tubes that meet requirements of standards were rolled with adoption of the proposed recommendations: the act of implementation of the results of the dissertation work on LLC "VO OSCAR" from 11. 11. 2019.
Key words: titanium alloys, deformation, mechanical and processing characteristics, texture, structure, contractive strain ratio.
