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Friction surfacing of titanium grade 1 and Ti-6Al-4V
Citation Link: https://doi.org/10.15480/882.1338
Publikationstyp
Doctoral Thesis
Date Issued
2017
Sprache
English
Author(s)
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2016-12-05
TORE-DOI
The friction surfacing process is a relatively novel and promising surface modification technology, by which coatings can be deposited as a protection or surface repair method. The main feature of this process, compared with other technologies, is that the coatings are deposited in solid state phase. Therefore, the induced massive deformation alters the initial microstructure of the materials, resulting in a fully recrystallised microstructure of the coatings. Typically, the grain size of the coating is smaller than that of the raw material, which leads to improved mechanical properties. Since the process is a relatively new technology, several possible material combinations in similar or dissimilar configurations are unexplored. Titanium alloys are rather expensive. Therefore, new technologies are required to keep the production cost at an acceptable level and offer an additional cladding process that is environmental friendly.
The aim of the current work was to deposit coatings from the titanium alloys by friction surfacing. Process development for Ti-6Al-4V alloy and Ti-Gr.1 as coating materials to be deposited by friction surfacing was carried out. At high temperatures titanium alloys exhibit complex deformation behaviour, particularly when passing through the alpha-beta phase transformation and in the beta phase state. Strain rate sensitivity and flow instabilities are characteristics of Ti-based materials that may hinder the deposition process. These difficulties were overcome by the selection of an adequate process control method and a systematic choice of process parameter combinations. A broad range of parameter sets for titanium depositions has been established, whereby two different acting rotational speed regimes were observed. The low rotational speed regime revealed variations in the process temperature, which influenced the material flow behaviour leading to flash generation at the coating. The microstructure in this regime consists of refined dynamically recrystallised grains. In contrast, the high rotational speed regime revealed a higher resulting temperature, which did not vary in this range. This constant temperature led to stable material flow behaviour and flash-free coatings were deposited. However, the high temperature influenced the grain size of the coatings resulting in coarse grains. Still, these differences in the grain size did not influence the fretting wear behaviour of the coatings. The investigation of fretting wear experiments exposed a similar behaviour of friction surfacing coatings and the base material. In micro tensile tests the coatings exhibited an increase in strength but a decrease in ductility, which is typical for dynamically recrystallised materials, which contain residual deformation. Therefore, it could be shown that friction surfacing can be considered as a repair method for titanium parts.
The aim of the current work was to deposit coatings from the titanium alloys by friction surfacing. Process development for Ti-6Al-4V alloy and Ti-Gr.1 as coating materials to be deposited by friction surfacing was carried out. At high temperatures titanium alloys exhibit complex deformation behaviour, particularly when passing through the alpha-beta phase transformation and in the beta phase state. Strain rate sensitivity and flow instabilities are characteristics of Ti-based materials that may hinder the deposition process. These difficulties were overcome by the selection of an adequate process control method and a systematic choice of process parameter combinations. A broad range of parameter sets for titanium depositions has been established, whereby two different acting rotational speed regimes were observed. The low rotational speed regime revealed variations in the process temperature, which influenced the material flow behaviour leading to flash generation at the coating. The microstructure in this regime consists of refined dynamically recrystallised grains. In contrast, the high rotational speed regime revealed a higher resulting temperature, which did not vary in this range. This constant temperature led to stable material flow behaviour and flash-free coatings were deposited. However, the high temperature influenced the grain size of the coatings resulting in coarse grains. Still, these differences in the grain size did not influence the fretting wear behaviour of the coatings. The investigation of fretting wear experiments exposed a similar behaviour of friction surfacing coatings and the base material. In micro tensile tests the coatings exhibited an increase in strength but a decrease in ductility, which is typical for dynamically recrystallised materials, which contain residual deformation. Therefore, it could be shown that friction surfacing can be considered as a repair method for titanium parts.
Subjects
Friction surfacing
Titanium
DDC Class
620: Ingenieurwissenschaften
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Friction Surfacing of Titanium Grade 1 and Ti-6Al-4V.pdf
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