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Abstract

For a number of years, the rise in the number of titanium alloy grades and therefore of microstructures has hampered the productivity of titanium parts. In order to understand the phenomena involved, this study presents a comparison of the chip formations between two microstructures obtained from the same alloy. The first part presents the two alloys, their microstructures and their methods of production. The chip formation of each material is then presented and shows two completely different processes. The first process is classical, for which shear mechanisms appear to be cyclical. Conversely, the second process depends on the orientation of the microstructure when the shear occurs. For a better understanding of the phenomena, the effect of cutting speed and feed is also discussed. Finally, in the last section, chip formations for the two microstructures are summarized and perspectives are presented.

Keywords

Titanium alloys machining chip formation Ti64 β structure

Introduction

For many years in the aeronautical industry, the machining of titanium alloys has been very problematic due to their low machinability. Moreover, the high diversity of alloys (Ti-64, Ti-1023, Ti-5553, Ti-17, etc.) does not allow application of the same cutting conditions or the same cutting tools on all titanium alloys. Different points explain this low machinability. The first is its low thermal conductivity which is always lower than the cutting conductivity of the cutting tool material. Consequently, the temperature is directed to the tool and rapid wear occurs. The second point is the chemical affinity of the titanium alloys with the cutting tool materials, favoring the diffusion of wear and limiting the tool life. Added to this is the behavior of titanium: its high mechanical properties and its high surface integrity sensitivity. To control these points, the cutting conditions chosen are always very low, reducing productivity. Over a number of years, certain works have explored chip formation for different alloys. The first among them focused on Ti64, an α + β structure, and were conducted by Komanduri and Von Turkovich,¹ Komanduri² and Cotterell and Byrne.³ These works describe chip formation in a homogeneous structure where the cutting process is never modified by material heterogeneity. Other works addressed chip formation during titanium alloy machining, with the turning of $β$ metastable alloy,^4,5 in milling of Ti1023⁶ or in turning with high pressure lubricants.⁷ However, all these articles concern the machining of bi-modal structures where $α$ nodules occur in the beta matrix (Figure 1).

Figure 1.

Chip formation during Ti1023 milling when (a) $t_{u} = 0.05 mm$ and (b) $t_{u} = 0.3 mm$ .⁶

The aim of this work is to provide a comparison of the chip formation of two structures generated with the same alloy. After the experimental set-up presentation and the highlighting of differences between the two structures, the chip formation for each structure is exposed. The following section concerns the effect of the cutting conditions on chip formation and chip geometry. The relation between chip formation and cutting conditions is also explained by the Oxley model.⁸ Finally, all results are summarized in the conclusion.

Experimental set-up

All tests have been carried out on CNC lathe Somab Genimab 900. The inserts used were CCMX 120408 with TiN PVD coating, the rake angle was 20° and inserts had a chamfer edge preparation of 0.02 mm. The tool material and geometry were classical for titanium machining. To simplify the analysis, all tests were carried out in orthogonal cutting configuration and in dry machining. The cutting conditions were defined according to the French Tool Material Pair standard⁹ and they are summed up in Table 1.

Table 1.

Cutting conditions for each test.

Test	$V_{c} (m mi n^{- 1})$	$t_{u} (mm)$
1	40	0.07
2	50	0.07
3	65	0.07
4	65	0.1
5	65	0.13
6	65	0.16
7	65	0.19

The cutting forces were measured using a KISTLER quartz three-component dynamometer type 9129A. Cutting force acquisition was carried out with Dynoware software. The cutting forces are separated into two components: F_r and F_c which are, respectively, the component co-linear to the feed direction and to the cutting speed direction. All tests and all measures were performed three times and the standard deviation is often lower than 5% of the range.

The recrystallization process comprises different steps and forms the Ti64 microstructure. Figures 2 and 3 show the heat treatment and the microstructure analysis. The aim of this section is to outline the heat treatment and the different phases of the titanium alloys obtained.

Figure 2.

Ti64 $α + β$ microstructure (forging process, microstructure, scheme of microstructure).

Figure 3.

Ti64 $β$ microstructure (forging process, microstructure, scheme of microstructure).

For this study, the classical structure is obtained with all heat treatments made below the transus temperature. As presented by Wanhill, some $β$ phases retained phases nodules are in the $α$ matrix (Figure 2). The Ti64 $α + β$ structure is explained by the rapid hardening in the $α + β$ domain.¹⁰

In opposition, the Ti64 $β$ structure is totally lamellar (Figure 3). As explained previously, this structure is obtained with the slow hardening from the $β$ domain after the forging process. The $α$ phases transform to acicular $α'$ structure in the beta matrix.¹¹ The slate diameters are a function of the cooling rate. When this rate decreases, the diameters increase until wide lamellae are obtained. The structure here is lamellar. The primary $α$ slate amalgamated to the $β$ grains are obtained when the recrystallization process is made in $α + β$ domain. During the cooling, the secondary $α$ lamellae are trapped into $β$ grains. The additional elements migrate into both phases. For example, the aluminum migrates into primary $α$ nodule contrary to the vanadium which go into $β$ phases.¹²Figure 3 shows the phase $α_{BG}$ (primary lamelar α phase in boundary grains) near to the $β$ grain joint. It occurs as continuous line around the old grain. Concerning the phase $α_{BG}$ , it germinates from the seal of the grain to the center and occurs in the form of slate. Finally, the $α_{WI}$ (intragranular primary lamelar α phase) phase germinates inside the old $β$ grain. All these phases are surrounded by the $β$ matrix.

The mechanical properties for the Ti64 $α + β$ are $R_{m} = 1100 MPa$ , $VHN = 349 HV$ and for the Ti64 $β$ $R_{m} = 1050 MPa$ and $VHN = 338 HV$ .

Cutting forces

First, cutting forces were compared between the two alloys (Figure 4). The monitoring of cutting forces serves to characterize the titanium’s behavior during machining. Concerning the Ti64 $α + β$ , the two components ( $F_{r}$ and $F_{c}$ ) are constant when the cutting speed increases. The component co-linear to the cutting edge is non-existent due to the orthogonal cutting configuration. The same evolution of cutting forces during Ti64 $β$ is observed. This stability is due to the low effect of temperature on titanium’s mechanical properties. Indeed, the titanium is generally used for parts where the temperatures are high and where the material must retain its properties. Consequently, the temperature’s increase produced by the highest cutting speed is never enough to reduce the mechanical properties of the titanium and hence the cutting forces. During the Ti64 $α + β$ machining, $F_{c}$ , which is the highest component, increases linearly with the feed, unlike $F_{r}$ which remains steady stable. The cutting force orientation $F_{r} / F_{c}$ has a significant impact on titanium machining because an increase of this point signifies an increase of the radial component and consequently a higher impact on surface integrity. Moreover, control this point can be used to monitor the tool wear as shown by Wagner et al.⁴ This $F_{r} / F_{c}$ cutting force orientation is explained by the cutting edge geometry which has a significant impact on the titanium machining, especially when it is higher than the feed.^4,13 Indeed for a feed lower than the cutting edge preparation, the material is trapped under the cutting edge which generates a dead zone where the strain rate become almost zero. The radius then becomes the main cutting face. Nevertheless, there is a major difference between the two alloys. The component $F_{r}$ is always lower than the $F_{c}$ component for the $β$ structure. Consequently, the surface integrity can be totally modified. This alloy has a $β$ phase density higher than the bi-modal initial structure. The hardness of the $β$ phase is higher compared to the $α$ phase,⁵ the machined surface is smaller and consequently the effect of the cutting edge is reduced.

Figure 4.

Effect of cutting speed and feed on cutting forces for Ti64 $α + β$ (a + b) and Ti64 $β$ (b).

Chip formation for Ti64 $α + β$ and Ti64 $β$

This section focuses on the study of the chip formation. The first structure is the Ti64 $α + β$ structure. As seen in Figure 5, the chip analysis clearly shows the presence of the primary and the secondary bands. In the primary shear bands, all these phases are sheared in one direction which corresponds to the shear angle (Figure 5).

Figure 5.

Chip formation during Ti64 $α + β$ machining.

The chip formation corresponds to assessments made by Komanduri and Von Turkovich¹ where the chip formation is described in several steps (Figure 5): (1) represents the chip’s undeformed surface. (2) is the $α$ section of the primary shear plane. This zone is a part of the catastrophic shear zone, which is separated from the previous segment. (3) is the zone where an intense shear band is formed by catastrophic shearing during the failure stage of the segment formation. (4) is the zone in contact with the rake face where intense shearing occurs. (5) is the primary shear plane where intense localized deformations appear. As described by Komanduri and Von Turkovich,¹ the primary shear plane is curved. (6) is the machined surface. To complete the understanding of the chip formation, the strain and the temperature were measured in situ. This study shows a strong relation between the cutting conditions and the temperature inside the workpiece material. Although averaged, temperatures are always lower than transus transformation temperatures.¹⁴

For the second structure $(α + β)$ , the chip formation and especially the shear band formation are different. They are not dependent on the shearing generated between the tool edge and the free surface of the chip. Indeed, several phenomena were observed due to the alloy structure which is composed of lamellar colonies $α + β$ with different orientations. These observations show that shear band formation is a function of colony orientation. Figure 6 shows various shear phenomena observed in the same chip. As seen in Figure 6, the chip geometry evolves and shows the variation in the chip formation.

Figure 6.

Chip morphology for Ti64 $β$ .

As seen in Figure 6, four configurations are identified:

First configuration. For all cutting conditions, some cracks may be created close to the primary shear band (Figure 6). Two causes are also identified. The first is comparable to the bi-modal structure $(α + β)$ and is due to high shear strains which occur in the material.¹ The second is only observed on this structure. Colony 1 compared to Colony 2 and Colony 3 compared to Colony 4 are strongly disoriented (Figure 6). The cracks are also explained by the difficulties producing dislocation between two colonies, as the microstructure analysis shows a strong difference of orientation of the Burger vector.¹²

Second configuration. The primary shear bands spread preferentially through transverse colonies (Figure 6, blue zone). This preference is explained by the existing stress gradient between the different lamellae with the highest value located at the interface. So, the deformation needed to shear the interface is greater than the deformation required to shear the $α$ lamellae located at the interfaces.

Third configuration. Transverse shear bands may occur when the colonies are co-linear to the shear band direction. This shearing is imposed by the motion between surrounding colonies. Indeed, two shearing directions are observed. The first is co-linear to the upper grain boundary, whereas the second direction is co-linear to the interface between the observed colony and the secondary shear zone.

Fourth configuration. Even though the chip formation can be assimilated to the segmented chip, a continuous shearing can still occur. This phenomenon is mainly observed near the free edge of the upper section of the chip. This shearing is explained by the motion of the highest colony (upper green arrow) and the lowest colony (lower green arrow).

The secondary shear zone is difficult to study because the thickness is variable due to the structure. However, the phenomena observed are similar to those explained by Komanduri and Von Turkovich¹ where a strong shearing co-linear to the chip velocity is observed.

Cutting conditions effect

The next section focuses on the effect on the feed and cutting speed on the chip formation. For each cutting condition, the first analysis was carried out on Ti64 $α + β$ , followed by Ti64 $β$ .

Cutting speed effect

Ti64 $α + β$

Concerning the $α + β$ alloy and for the first cutting speeds when $tu = 0.07 mm$ , the primary shearing is continuous. Indeed, and as seen in Figure 7, all the $α$ phases are sheared in the same direction and the chip is not segmented.

Figure 7.

Chip morphology when $V_{c} = 40 m mi n^{- 1}$ and $t_{u} = 0.07 mm$ for Ti64 $α + β$ .

When the cutting speed increases $(65 m mi n^{- 1})$ , the small rise in shear force is sufficient to generate some adiabatic shear bands. It should be noted that the frequency of adiabatic shear band formation is enhanced. However, the chip morphology is not homogeneous because some continuous chip sections occur (Figure 8).

Figure 8.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ and $t_{u} = 0.1 mm$ for Ti64 $α + β$ .

Using the Oxley model,⁸ it is possible to define the shear force $(F_{s})$

F_{s} = F_{c} \cos (ϕ) - F_{r} \sin ϕ

(1)

$F_{s}$ is two times larger when $V_{c} = 50 m mi n^{- 1}$ than when $V_{c} = 40 m mi n^{- 1}$ (Table 2). The plastic work increases (mostly converted into heat) and generates a thermal softening leading to shear band formation and consequently to chip segmentation. The alloy between the primary shear bands is oriented along the primary bands. The material is also deformed in this zone.⁴ Indeed, the $β$ phase size is often greater than the uncut chip thickness and consequently it is also cut or twinned. Between $V_{c} = 50 m mi n^{- 1}$ and $V_{c} = 40 m mi n^{- 1}$ , the shear angles do not change. Consequently, the strong increase in shear force generates the highest energy production (mostly thermal energy) in the primary zone.

Table 2.

Evolution of shear force and chip thickness for Ti64 $α + β$ .

$V_{c}$	$t_{u}$	$ϕ$	$t_{\max}$	$t_{\min}$	$F_{s}$
40	0.07	39	95	80	49
50	0.07	35	92	58	112
65	0.07	34	95	65	120

The maximal chip height (between chip base and the highest chip segment) is stable whatever the cutting speed. However, the minimal height decreases drastically between 40 and 50 m min⁻¹. Indeed, adiabatic shear bands occur and generate some segments in the chip.¹ The minimal length evolution is also due to two phenomena:

The deformed segments (mostly sheared), which is a function of the shear band formation frequency;

The intensity of cracking formation due to the compression which occurs under the surface to be machined.

Consequently, between a continuous chip and a segmented chip, the minimal height decreases. Between two chips segmented with different cutting conditions, the height increases with shear band frequency. It should be noted that this supposition must be considered only when the cracking mechanisms are the same (same cutting forces, as in this study). The segment formation is explained in Figure 9. Point A, located initially at the intersection between the chip roots and the alloy (at the free surface), moves when the tool feeds (a) and some segments occur in the chip (b and c). When the frequency of adiabatic band formation increases, the minimal height of the chip $(t_{\min 3})$ is higher than $t_{\min 2}$ is when the distance between two shear bands is lower (c). So, the minimal height of the chip increases when the cutting speed is $V_{c} = 65 m mi n^{- 1}$ .

Figure 9.

Impact of frequency on minimal thickness of chip: (a) initial state, (b) low-frequency segmentation and (c) high-frequency segmentation.

Concerning the secondary shear zone, it increases with the cutting speed. Indeed, the secondary shear zone thickness rises when the cutting speed grows. The rise in sliding speed due to a higher cutting speed generates a greater gradient velocity. Actually, the variation increases because the speed at the chip interface is equal to zero, unlike the one located at the highest point of the chip. The chip thickness, affected by the velocity gradient, increases with the sliding speed and coincides with the secondary zone thickness. The same observations have been made by Wagner and colleagues^4,6 for two different titanium alloys, Ti1023 and Ti5553.

Ti64 $β$

The analysis of the Ti64 $β$ alloy is different because the chip formation is a function of the structure encountered by the primary shear zone during its formation. Consequently, for the same cutting speed, different phenomena are generated. For each cutting condition, two pictures of chips are given and show the different chip morphology according to the observed point. For the lowest cutting speed, only a few adiabatic shear bands are observed (Figure 10(a)). These bands are always located in the lamellar colonies oriented transversely to the primary shear bands. In the remainder of the chip where the adiabatic shear bands are not generated, a continuous chip is observed. However, a section of the material never seems to be sheared, unlike in the previous structure. This unsheared area is located at the old $β$ grain. Even though the shear generated for the lowest cutting speed is small, it is enough to shear transverse colonies by bands (Figure 10(b)). Moreover, the lamellae whose initial orientations are almost identical to the shear angle all appear to be parallel and oriented along the shear angle.

Figure 10.

Chip morphology when $V_{c} = 40 m mi n^{- 1}$ and $t_{u} = 0.07 mm$ for Ti64 $β$

When $V_{c} = 50 m mi n^{- 1}$ , some wider bands are generated. This increase is due to higher shearing forces (Table 3) and a slight difference in the colony’s inclination. Moreover, the tests show that the thickness of the primary shear bands may be smaller when a transversal colony is surrounded by collinear colonies (Figure 11(a)). The transversal colonies impose the formation of adiabatic shear bands and consequently a segmented chip. Some cracks are also created. They are due to the strain concentration at the colony interfaces. When a colony parallel to the primary shearing occurs within the entire chip thickness, adiabatic shearing and chip segmentation are never generated. The chip is also continuous with some strong cracks.

Table 3.

Evolution of shear force and chip thickness for Ti64 $β$ .

$V_{c}$	$t_{u}$	$ϕ_{s}$	$t_{\max}$	$t_{\min}$	$F_{s}$
40	0.07	33	97	46	400
50	0.07	32	109	50	385
65	0.07	30	99	40	400

Figure 11.

Chip morphology when $V_{c} = 50 m mi n^{- 1}$ and $t_{u} = 0.07 mm$ for Ti64 $β$ .

For the upper cutting speed $(V_{c} = 65 m mi n^{- 1})$ , the chip formation is almost similar (Figure 12). The main difference is in the band thicknesses. Indeed, they are thinnest, despite a higher shearing force. Contrary to the previous cutting conditions, some adiabatic shearing bands occur even if parallel colonies are predominant.

Figure 12.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ and $t_{u} = 0.07 mm$ for Ti64 $β$ .

As with the previous structure (Ti64 $α + β$ ), the increase in cutting speed modifies the chip formation. For higher cutting speeds, the thermal energy increases and results in some adiabatic shear bands. Concerning the chip geometry, the effect of cutting speed is very low. The maximum chip thickness $(t_{\max})$ and the minimum chip thickness $(t_{\min})$ are stable. Despite the heterogeneity of the microstructure, the shear angle is also stable. These results show the low effect of cutting speed on the chip formation.

Feed effect

This section concerns the effect of feed on the chip morphology. As with the previous structure, the analysis was conducted first on the Ti64 $α + β$ structure and next on the other structure.

Ti64 $α + β$

When the feed exceeds $0.10 mm t r^{- 1}$ , the chips become exclusively segmented. Indeed, some adiabatic shear bands are observed (Figures 13 and 14). However, the frequency of shear bands becomes constant when the feed exceeds $0.13 mm t r^{- 1}$ .

Figure 13.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ , $t_{u} = 0.07 mm$ and $t_{u} = 0.13 mm$ for Ti64 $α + β$ .

Figure 14.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ , $t_{u} = 0.16 mm$ and $t_{u} = 0.19 mm$ for Ti64 $α + β$ .

For the upper feed, the frequency and the shear angle are stable. Concerning the shear forces, their values increase with the feed (Table 4). The dissipated energy is higher. This affects the thermal softening and the shear band generation is constant. Moreover, when the feed exceeds $0.13 mm t r^{- 1}$ , some crack formations occur near the shear bands. Their depths increase linearly with the feed and seems to be stable when the feed is over $0.16 mm t r^{- 1}$ . These cracks are generated when the shear stress in the bands is above the material shear strength. Consequently, their development is a function of the increase in shear force due to the feed. Finally, the secondary shear zone thickness is a function of the feed. The cutting force increases with the speed. Consequently, the normal strain applied on the chip surface (at the tool–chip interface) is higher. The velocity gradient is thus modified. Indeed, the speed at the tool–chip interface is always zero, but the maximal speed value along the thickness is obtained at a greater height. The secondary shear thickness is thus greater.

Table 4.

Evolution of shear force, chip thickness and shear angle for Ti64 $α + β$ .

$V_{c}$	$t_{u}$	$ϕ$	$t_{\max}$	$t_{\min}$	$F_{s}$
65	0.07	34	95	65	120
65	0.1	31	145	83	342
65	0.13	31	227	137	491
65	0.16	32	247	84	568
65	0.19	32	263	107	682

Ti64 $β$

Concerning the $β$ alloy, when the feed increases from 0.07 to 0.1 mm tr⁻¹, the thickness removed is in the range of the medium size of the lamellar colonies. The probability of shearing several colonies in the same thickness increases.

The chip shown in Figure 15(a) explains the complexity of the chip formation which occurs in this material. Indeed, due to the increase in feed, some colonies occur on the chip which are positively oriented for the shearing bands (transversal colonies). There is the significant presence of a hardness phase and of some colonies, which are collinear to the shearing band generation. Consequently, the chip is irregularly segmented with some strong strain concentrations and so some cracks. The chip morphology is also imposed by the nodule size. Moreover, the shearing forces (Table 5) are not sufficient to impose a constant shearing band generation.

Figure 15.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ and $t_{u} = 0.1 mm$ for Ti64 $β$ .

Table 5.

Evolution of shear force, chip thickness and shear angle for Ti64 $β$ .

$V_{c}$	$t_{u}$	$ϕ$	$t_{\max}$	$t_{\min}$	$F_{s}$
65	0.07	30	99	40	400
65	0.1	22	82	15	640
65	0.13	28	134	47	704
65	0.16	30	219	184	770
65	0.19	20	208	16	1100

However, the observation of segments mainly comprising transversal colonies shows an increase in crack depth along the shearing bands (Figure 15(b)). When the feed increases to $0.13 mm t r^{- 1}$ , some unfavorably oriented adiabatic bands are generated in the colonies (Figure 16(b)).

Figure 16.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ and $t_{u} = 0.13 mm$ for Ti64 $β$ .

The size of the cracks is still greater. This is due to the increase in shearing forces and the existence of many colonies which are unfavorably oriented to each other in the same thickness. The heterogeneity of some nodules or old $β$ grain boundary generates the decrease in shearing band width. Consequently, colonies transverse to the shearing (upper part of the chip 16 (a)) bands are not segmented. For the highest feed $(0.16 mm t r^{- 1})$ (Figure 17(a)), the increase in shearing forces brings a regularity in the chip formation. Indeed, the frequency of the shear band generation seems constant. The segment cracks are larger due to higher shearing forces and a greater number of interfaces between colonies in the same thickness. The chip generated when $f = 0.19 mm t r^{- 1}$ is similar to the previous feed (Figure 17(b)). The distance between shearing bands and the segmentation is constant. The chip formation also seems stable. Moreover, the crack height is constant between these two feeds despite the increase in shearing forces. Finally, the relationship between the feed and the shear angle is not direct. This variation is explained by the non-homogeneous structure.

Figure 17.

Chip morphology when $V_{c} = 65 m mi n^{- 1}$ ; $t_{u} = 0.16 mm t r^{- 1}$ and $t_{u} = 0.19 mm t r^{- 1}$ for Ti64 $β$ .

Conclusion

The article presents a study of the chip formation of two structures obtained from the same alloy. The study is broken down into two sections.

The first concerns the chip formation of a two-phase structure: the Ti64 $α + β$ titanium. The chip formation in this alloy follows patterns outlined in the literature. Two specific zones are easily identified: the primary and the secondary shear zones where the material is sheared in a single direction. The chip generated is mainly a saw-tooth chip whose formation is largely influenced by the feed.

The second section describes the analysis of the chip formation of a specific structure obtained from the same alloy. Indeed, contrary to the previous structure, it is not homogeneous. Some zones are observed where the structure is different. This heterogeneity generates a specific chip formation. The study of the chip formation shows that the primary shear band formation is a function of the cutting conditions, but especially a function of the relation between the primary shear band direction and the lamella inclinations. For example, for a single colony, if the primary shear band direction is collinear to the lamellae, a continuous chip is generated, while if the shear band direction is transverse to the colony, a shear band is created and the chip is a saw-tooth chip.

This study shows that the machining of titanium alloy is a function of the microstructure, and this dependency can lead to non-classical phenomena during chip formation. Moreover, this study emphasizes the need to develop new behavior laws which include material heterogeneity to improve machining modeling of these materials. Finally, as mentioned in section “Introduction,” the surface integrity of titanium alloys is very sensitive, thus phenomena observed within the chip can also be generated in the machined surface and need to be studied.

Footnotes

Appendix 1 Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship and/or publication of this article.

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Comparison of the chip formations during turning of Ti64 β and Ti64 α + β

Abstract

Keywords

Introduction

Experimental set-up

Cutting forces

Chip formation for Ti64 α + β and Ti64 β

Cutting conditions effect

Cutting speed effect

Ti64 α + β

Ti64 β

Feed effect

Ti64 α + β

Ti64 β

Conclusion

Footnotes

Appendix 1

Declaration of conflicting interests

Funding

References

Chip formation for Ti64 $α + β$ and Ti64 $β$

Ti64 $α + β$

Ti64 $β$

Ti64 $α + β$

Ti64 $β$