This comprehensive summary of the current state of the art of titanium addresses all aspects of titanium. It is all covered, from the magical metal's basic characteristics and physical metallurgy to the correlations between processing, microstructure and properties. Richly illustrated with more than figures, this compendium takes a conceptual approach to the physical metallurgy and applications of titanium, making it suitable as a reference and tutorial for materials scientists and engineers. Richly illustrated, this compendium takes a conceptual approach to the physical metallurgy and applications of titanium, making it suitable as a reference and tutorial for materials scientists and engineers.
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The static preload F stat. A limiting number of cycles to run out of 2. In addition, the Smith diagram was used to predict the fatigue life. The alpha lamellae width has a significant influence on fatigue life. It is assumed that the increasing width of alpha lamellae decreases fatigue life. A comparison of fatigue results with given alpha lamellae width in our material to the results of other researchers was performed.
The SEM fractography was performed with an accent to reveal the initiation sites of crack at low and high load stresses and mechanism of crack propagation for the fatigue part of fracture. The TiAl6V4 alloy has a relatively high resistance in cyclic loading [ 1 — 4 ]. However, the course of fatigue damage, however, depends on the content of the additive elements, microstructure, surface treatment, and size and type of applied stresses.
The greater the roughness of the surface, or the surface saturated with oxygen or nitrogen, the worse the fatigue properties of titanium. The fatigue range for titanium alloys is reached at 10 6 7 cycles, but it is dependent on the load frequency [ 5 ]. Generally, the grain size of materials is a very important characteristic of fatigue life. Likewise, the fatigue strength increases after increasing strength via work hardening.
In addition, Gao et al. Another research was performed by Peters et al. For the fatigue process as itself, it is a well-known fact that most of the fatigue cracks initiate at free surface due to surface roughness, oxide presence, or carbide particles. This phenomenon occurs only in special cases when a very high-cycle fatigue test over 10 9 cycles to failure is performed at low-stress amplitude.
Zuo et al. This kind of initiation was not confirmed at low-cycle or high-cycle fatigue of TiAl6V4 alloy. They have shown that fatigue crack initiation sites are related to microstructure. The second type of the fatigue crack initiation site is for equiaxed structures. Therefore, fatigue strength is affected by the grain size and on grain size is yield stress dependent as well. The third type of the fatigue crack initiation site is for duplex structures.
Kuhlman [ 12 ] showed that the fatigue crack initiation site also depends on the cooling rate. Boyer and Puschnik et al.
The influence of microstructure on fatigue properties of Ti6Al4V alloys at high-cycle fatigue is discussed in the works of Wu et al. Their results prove the fact that various microstructures decrease from bimodal, lamellar to equiaxed high-cycle fatigue strength. In the initial stage, the high-cycle fatigue strength increases. However, it gradually decreases with increasing amount and size of the primary alpha phase. A similar effect of decreasing high-cycle fatigue strength can also be observed in the case of equiaxed or lamellar microstructures of Ti6Al4V alloy.
Essentially, it can be generalized that the fatigue strength of the Ti6Al4V alloy decreases, either due to the increase in the alpha-phase grain or by increasing the width of the alpha-phase lamellae. Another factor affecting the fatigue strength of the Ti6Al4V alloy is the load frequency. This issue was studied by Furuya and Takeuchi [ 17 ]. However, this is only true if the fatigue crack has initiated below the alloy surface.
Morrissey and Nicholas [ 18 ] also studied the impact of load frequency on strain rate or temperature increase due to internal damping. According to their data comparison, there are no frequency effects. The comparison of S-N results at ultrasonic and conventional frequencies is shown in Figure 1. There is an assumption that bending load should decrease fatigue life of alloy due to more complex stress course in the specimen. HX are given in Table 1.
The alloy was in the annealed condition. According to its work, the most suitable treatment for increasing the fatigue properties and achieving the reasonable fatigue crack growth is mill annealing MA or A. The microstructure of experimental material is shown in Figure 2. The sample was next rinsed in warm water and alcohol and dried after each step. Two single-disk MTH polishers were used for polishing. The disk was moistened with alcohol during polishing, and the sample was polished against the counterclockwise rotation of the disc.
In the second step, the D07 paste with a diamond grain size of 0. The sample was rinsed in warm water and alcohol and dried after each step. One side of the specimen was over polished due to the good observation of fatigue crack propagation. The specimens were numbered from 1 to It provides fatigue testing of materials and components, e. Tests can also be carried out under various environmental conditions, e. In addition, torsion and bending tests can also be carried out. The parameters of the test were set as follows: the static preload force F stat.
For titanium alloys, this value is considered as the fatigue limit if the specimens withstand the 2. To prevent specimens heating during the fatigue test, the specimens were cooled by an external fan. The S-N curve was drawn. It means that the specimen is preloaded by negative static force with a higher value than the stress amplitude which results in more complex loading in the center of the specimen.
There is an expectation that fatigue life shifts to lower values due to more complex loading compared to push-pull results. Metallography specimens were prepared by cutting with MTH Micron precise saw and then mounting into bakelite mixture in Struers CitoPress 1 and finally ground and polished using Struers TegraSystem TegraPol and TegraForce-1 and a special program for titanium alloys.
Grinding and polishing consist of a few steps: grinding with SiC sandpaper No. This procedure was applied on specimens for light microscopy LM and for scanning electron microscopy SEM analysis as well. The microstructure was observed on light microscope Neophot The microstructure of experimental material is documented in Figures 2 and 4. The average length of the grains is The larger the lamella dimensions are, the lower the fatigue life of the alloy is. To confirm this phenomenon, it would be advisable to perform tests for a more fine-grained structure and to compare the obtained values.
The S-N curve is shown in Figure 5. The experimental data were interpolated and the following coefficients of the Basquin [ 23 , 24 ] equation were obtained:. The results for all specimens used at the fatigue test with specimen numbering are shown in Table 2. The results comparison shows a difference about This result shows a more complex character of fatigue specimens loading than simple push-pull loading.
The three-point bending loading includes a compression loading and a tension loading as well, and the specimen is subjected not only to direct stress but to bending moment with increasing value when approaching the specimen centre. The diagram is designed for the compressive stress area, and therefore, it is advantageous for its construction to use the values of the yield bearing strength and ultimate bearing strength [ 26 ] that involve a more complex load.
Figure 7 shows the fracture surface where the fatigue region, static break area, and a fatigue crack initiation site are marked black arrow. In Figure 8 , the images of samples No. The fatigue crack in both cases initiated at the free surface of the polished samples at the sites of the highest concentration of stress. Major crack propagation proceeded from the free surface by transcrystalline cleavage of TiAl6V4 alloy grains with the cleavage facets observed at the crack initiation site.
The cleavage facets of samples 9 and 7 are shown in Figures 8 c and 8 d. Micro-fractographic images of cleavage facets created by transcrystalline cleavage of TiAl6V4 alloy grains along the direction of propagation of the magistral fatigue crack are notable in Figure 9. In Figure 9 a , the transcrystalline cleavage facet with river morphology is visible.
The origin of the rivers also means energy consumption, which slows down the rate of propagation of the fatigue crack tip. In the area of the stable fatigue crack propagation, the striations Figure 10 a are visible on the surface, indicating the position of the crack tip at the given moment and creating ridges spreading from the initiation site. These ridges are perpendicular to the direction of magistral fatigue crack propagation.
Another characteristic feature of the fatigue process is the secondary crack parallel to the advancing fatigue crack front documented in Figure 10 b. From the comparison of the individual micrographs, it is clear that the amount of secondary cracks increases with the rising value of the stress amplitude.
The change in the direction of the striation propagation due to the change in the direction of the magistral fatigue crack growth is shown in Figure 11 a. The area of static failure documented in Figure 11 b is characterized by a transcrystalline ductile fracture with dimple morphology. A ductile fracture occurs by coalescence of microcells that nucleate at the grain boundaries, secondary-phase particles, or inclusions. Striations and secondary fatigue cracks, which are features of fatigue fracture, have also been observed in this area.
In the fatigue test, all specimens except of two which of course were not included in S-N curve results were polished. Specimen No. For specimen No. To explain this phenomenon, the hardness measurements of material were performed and the results of measurement are shown in Table 3.
The values are the mean values of four hardness measurements. The volumes of the k coefficient for various material types and their effect on final UTS were discussed more in detail in the work of Tabor et al. This difference in material toughness and hardness is possible due to secondary hardening, which was not reported in the material list. The fatigue life was reached after a 2. However, it is necessary to take into count the different loading modes, specimen shape, and surface finishing of samples used at push-pull loading.
The comparison with push-pull loading is performed due to the lack of data about the three-point bending fatigue test for this alloy in English.
Three-Point Bending Fatigue Test of TiAl6V4 Titanium Alloy at Room Temperature
This comprehensive summary of the current state of the art of titanium addresses, in varying levels of detail, all aspects of titanium, including: basic characteristics and physical metallurgy, the extractive metallurgy, the various production processes, the correlations between processing, microstructure and properties, and all aspects of applications including economic ones. Richly illustrated with more than figures, this compendium takes a conceptual approach to the physical metallurgy and applications of titanium, making it suitable as a reference and tutorial for materials scientists and engineers. In this Second Edition the authors included new information on topics that have emerged after the First Edition was completed and published in Richly illustrated, this compendium takes a conceptual approach to the physical metallurgy and applications of titanium, making it suitable as a reference and tutorial for materials scientists and engineers. It would be suitable for varying levels of people from postgraduate students just entering the titanium field, to experienced researchers and engineers. I started working with titanium in … but was still able to find much new and interesting information in this book.