A T.E.M. Study of the Microstructure of a Ti 48 Al 48 Cr 2 Nb 2 Alloy
- PDF / 2,269,168 Bytes
- 6 Pages / 412.74 x 641.7 pts Page_size
- 85 Downloads / 203 Views
vacuum arc melting furnace. Observations were also made in a specimen of this alloy treated l h at 1375°C, cooled in the furnace till 1250'C and then air-quenched. The aim of this last experiment is to investigate the orientations of the y lamellae just after their nucleation, namely before their joining. To perform such a statistical analysis in one grain requires numerous experiments and consequently such experiments cannot be repeated several times. It has been however verified that the present results are well representative of the specimen microstructure by qualitative observations and by statistical measurements performed in smaller areas. The procedure follows to distinguish the six orientation variants and the interface relation ships is described in detail in [4]. EXPERIMENTAL RESULTS Figure 1 shows a typical microstructure of the as cast Tia4 A148Cr 2Nb 2 alloy. The habit plane is edge on. The lamellae are very thin (their average width is 300 nm) with respect to their length and the interfaces are very flat lying parallel to each other. Several y lamellae are usually sandwiched between the %2 lamellae. It has been verified that the three interface relationships are present at the y/y interfaces. Inside the y lamellae, ordered domain boundaries separate the lamellae into areas having different orientation variants and belonging to the same orientation group. Contrary to the ordered domain interfaces, these boundaries are wavy.
Figure 1. Microstructure of the as cast Ti48AI48Cr 2Nb2 alloy.
U
Ogi
Quantitative analysis of the microstructureof the as castTi48Al 48 Cr2Nb2 alloy. The results which will be presented in this section were obtained in one area of 18.5 gm by 43 gim. The length (43 gm) is parallel to the habit plane. This area contains 80 lamellae, 20 of which are CC 2 lamellae. The volume fractions of the two phases are : Fv 2 = 5% and Fvy = 95%. The 60 y lamellae are distributed as follows : * 6 single lamellae which are bordered by two %2lamellae, * 3 pairs, each pair forming an y/y interface, 0 5 triplets, each triplet forming two yly interfaces, 0 3 quadruplets, each quadruplets forming three y/y interfaces, 3 areas containing each 7 lamellae joined together, thus forming each six y/y interfaces, 0 For each y lamella, the orientations were then determined. Tables 1 and 2 give the distributions in number and volume fraction of the groups of orientations and of the orientation variants, respectively. One of the two orientation groups is present on majority of cases. This result is quite different from that obtained in the Ti54-AI46 and PST alloys [4] where similar measurements have demonstrated that the two groups of orientations are approximately present at 50%. KK8.10.2
Table 1. Distribution in number and volume fraction of the two groups of orientations. I71
_I
Number
No
19
Totals
41
60
of lamellae
%
32
68
100
Volume
No(tm )
36.5
191.5
226
fraction
%
15
85
100
Table 2. Distribution in number and volume fraction of the six orientation variants.
OR I
OR 2
OR3
OR 4
Data Loading...
