Research of Materials Science March 2015, Volume 4, Issue 1, PP. 1-7
Phase Relationships in the Er-Si-Ti Ternary System at 773 K Xueqiang Li1,2,3,4, Jingqi Liu1,2,3*, Mengqi Tang1,2,3, Chunhui Li1,2,3 1. College of Materials Science and Engineering, Guangxi University, Nanning, Guangxi 530004, P.R. China 2. Institute of Materials Science, Guangxi University, Nanning Guangxi 530004, P. R.China 3. Key Laboratory of Nonferrous Metal Materials and New Processing Technology, Guangxi University, Ministry of Education, Nanning Guangxi 530004, P. R. China 4. The Second Technician Institute of Shaoguan, Shaoguan Guangdong 512031, P. R. China
Abstract The phase relationship in the Er-Si-Ti ternary system at 773 K was investigated mainly by X-ray powder diffraction analysis with the aid of scanning electron microscope analysis in this work. The existence of nine binary compounds Er5Si3, Er5Si4, ErSi, Er3Si5, Si2Ti, SiTi, Si4Ti5, Si3Ti5, SiTi3 and two ternary compounds ErSiTi and Er2Si4Ti3 was confirmed in this system at 773 K. The homogeneity range of Er3Si5 phase extended from about 63 at% Si to 66 at% Si in Er-Si system at 773 K. The homogeneity range of Si3Ti5 phase extended from about 62 at% Ti to 64 at% Ti in Si-Ti system at 773 K. The maximum solid solubility of Er in Si3Ti5 phase was found to be about 2 at% Er in Er-Si-Ti ternary system at 773K. At 773K, the isothermal section of phase diagram of the Er-Si-Ti ternary system was found to consist of fourteen single-phase regions, twenty-seven two-phase regions and fourteen three-phase regions. Keywords: Rare Earth Alloys and Compounds; Er-Si-Ti ternary System; Phase Diagrams; X-ray Diffraction; Scanning Electron Microscopy
1. Introduction The strengthening-mechanism of Ti-Si eutectic alloy is greatly different from the traditional titanium alloys. The eutectic alloy consists of two phases, one of them is a ductile phase α-Ti which is the matrix, and one of them is a brittle phase Si3Ti5 which act as the reinforcement. This composition is similar to the extensively applied Fe-C alloys and Al-Si eutectic alloys. The titanium–silicon eutectic alloy has excellent mechanical properties, chemical properties and casting properties. They were applied to aerospace engineering, petrochemical engineering, automobile and medical appliance, and so on [1-3]. However, its low temperature plasticity which is induced by the essential brittleness of Ti5Si3 intermetallic compound has severely limited the development of this alloy. Some studies reported that the microstructures and properties of titanium alloys may be improved; when the small amounts of rare earth (RE) element were added to titanium alloys [4-5]. The investigation of the phase diagram may provide useful information or searching new materials and give the guide for preparing high quality materials. Lately, the phase diagrams of the M-Si-Ti (M = La, Ce, Dy, Pr, Nd, Nb and Sn) ternary system were investigation [6-12]. Moreover, the magnetic properties of the compounds RESiTi (RE = Gd –Tm, Lu, Y) [13, 14] and RE2Si4Ti3 (RE = Gd - Er) [15] were studied. Up to now, the phase diagram of the Er-Si-Ti ternary system has not been reported. In this work, we investigated the phase relationship in the Er-Si-Ti ternary system at 773 K. The purpose of this work is to confirm the existence of the compounds and the isothermal section of the phase diagram of the Er-Si-Ti ternary system at 773 K, to provide useful information for searching new materials, or preparing pure and high quality materials.
2. Experimental details The purities of erbium, silicon and titanium used in this work are 99.9%, 99.99% and 99.99%, respectively. One -1http://www.ivypub.org/rms
hundred and ten alloy buttons, each weighing 2g, were prepared by in arc melting using a non-consumable tungsten electrode and a water-cooled copper tray under a high purity argon atmosphere. All samples were sealed in evacuated quartz tubes for homogenization heat treatment. The samples were homogenized at 1000 K for three weeks and then they were cooled to 773 K at a rate of 0.16 K/min, kept at 773 K for one week. Finally, all of the samples were quenched into liquid nitrogen. The samples were ground into powder for X-ray diffraction (XRD) analysis. The treated brittle alloy samples were ground into powder for XRD analysis. The non-brittleness powders were sealed in evacuated glass tube and annealed at 773 K for 3 days, followed by quenched into liquid nitrogen before X-ray diffraction experiment. XRD analysis was performed with powder using a Rigaku D/Max 2500V diffractometer with CuKα radiation, graphite monochromator, a voltage of 40 KV and a current of 200 mA. The materials data were analyzed by using JADE 5.0 ， software [16]，PCW ( Powder Cell Windows software) [17] and Pearson s Handbook of Crystallographic Data [18]. And a Powder Diffraction File (PDF release 2004) was used to determine the phase existence in each sample. Microstructures and fractograph were examined by using optical microscope, scanning electron microscopy (SEM, HITACHI S3400N) coupled with energy dispersive spectrometry (EDS).
3. Result and discussion 3.1 Intermetallic compounds and solid solubility In this work, at 773 K, the existence of four intermetallic compounds Er5Si3，Er5Si4, ErSi and Er3Si5 was confirmed in the Er-Si system , and Er3Si5 is a vacancy superlattice based on the AlB2 structure with one of 6 Si missing from each graphitic-like Si layer [19]; the existence of five intermetallic compounds Si2Ti, SiTi, Si4Ti5, Si3Ti5 and SiTi3 was identified in the Si-Ti binary system; no binary compound was found in the Er-Ti system; which agrees well with the results of Refs. [18-20]; the existence of two ternary compounds ErSiTi and Er2Si4Ti3 was confirmed which is in good agree the reported in Refs. [13-15]. The X-ray diffraction (XRD) patterns of the samples with compositions of Er10Si80Ti10 (1#), Er4Si48Ti48 (8#), Er4Si34Ti62 (10#), Er56Si40Ti4 (15#), Er44Si36Ti20 (36#), Er30Si50Ti20 (47#), and Er36Si20Ti44 (50#) were shown in Fig. 1 to Fig.7, respectively. XRD patterns of sample 1# consist of the patterns of Er3Si5 + Si + Si2Ti three phases. XRD Patterns of sample 8# consist of the patterns of Er3Si5 + SiTi + Si4Ti5 three phases. XRD patterns of sample 10# consist of the patterns of ErSiTi + SiTi3 + Si3Ti5 three phases. XRD patterns of sample 15# consist of the patterns of Er5Si3 + Er5Si4+ Er2Si4Ti3 three phases. XRD patterns of sample 36# consist of the patterns of Er5Si3 + ErSiTi + Si3Ti5 three phases. XRD patterns of sample 47# consist of the patterns of Er3Si5 +ErSi + Er2Si4Ti3 three phases. XRD patterns of sample 50# consist of the patterns of Er + Ti + ErSiTi three phases. XRD patterns and SEM photomicrograph of sample with compositions Er26Si54Ti20 (20#) were shown in Fig. 8 and Fig. 9, respectively. It consist of the patterns of Er3Si5 + Er2Si4Ti3 + Si4Ti5.
FIG.1 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er10Si80Ti10 (1 ): Er3Si5+Si+Si2Ti.
FIG.2 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er4Si48Ti48 (8 ): Er3Si5+SiTi+Si4Ti5.
The grey phase of in the SEM photomicrograph is Er2Si4Ti3 compound, the black phase of in the SEM photomicrograph is Er3Si5 compound and the white phase of in the SEM photomicrograph is Si4Ti5 compound, as Fig. -2http://www.ivypub.org/rms
9 shown. The energy spectrum of the grey phas and black phase of in the SEM Photomicrograph were shown in Fig. 10 and Fig. 11, respectively.
FIG.4 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er56Si40Ti4 (15 ): Er5Si3+Er5Si4+Er2Si4Ti3.
FIG.5 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # [Er-Ti-Si50.raw] 50 OF Er44Si36Ti20 (36 ): ErSiTi+Er5Si3+Si3Ti5.
FIG.6 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er30Si50Ti20 (47 ): Er2Si4Ti3+ErSi+Er3Si5.
I(Counts)
FIG.3 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er4Si34Ti62 (10 ): ErSiTi+SiTi3+Si3Ti5.
2000
0 00-0371> ErSiT i T his work 00-0381> ErSiT i Ref.[13] 65-6231> T i - T itanium 65-7248> Er - Erbium 20
25
30
35
40
45
50
55
60
2-Theta(째
FIG.7 XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er36Si20Ti44(50 ): ErSiTi+ Er+Ti.
FIG.8XRD PATTERNS OF THE SAMPLES WITH COMPOSITIONS # OF Er26Si54Ti20 (20 ): Er3Si5+Er2Si4Ti3+Si4Ti5.
FIG. 9 SEM PHOTOMICROGRAPH OF SAMPLE 20#, THE GREY PHASE OF THEM IS Er2Si4Ti3 COMPOUND, THE BLACK PHASE OF THEM IS Er3Si5 COMPOUND AND THE WHITE PHASE OF THEM IS Si4Ti5 COMPOUND. -3http://www.ivypub.org/rms
Element
Wt%
At %
Er L
50.07
17.94
Si K
22.17
47.32
Ti K
27.75
34.73
FIG.10 SEM PHOTOMICROGRAPH AND ENERGY SPECTRUM OF SAMPLE 20#, GREY PHASE OF THEM IS Er2Si4Ti3 COMPOUND.
Element
Wt%
At %
Er L
74.86
33.33
Si K
25.14
66.67
FIG.11 SEM PHOTOMICROGRAPH AND ENERGY SPECTRUM OF SAMPLE 20#, THE BLACK PHASE OF THEM IS Er3Si5 COMPOUND.
A.V. Morozkin reported the structure of the ErSiTi compound (space group: P4/nmm, structure type: CeFeSi, lattice parameter: a=0.3979nm, c=0.7433nm). The erbium and silicon atoms occupy the 2(c) site (1/4, 1/4, 0.652(4)) and (1/4, 1/4, 0.255(16)), respectively, and the Ti atom occupy the special position 2(a) (3/4, 1/4, 0) in the ErSiTi structure [13]. In order to agree well with the XRD patterns of ErSiTi phase in sample and PDF of the ErSiTi structure, we adjusted the sites of atoms occupy in the ErSiTi structure and the lattice parameter, i.e. reconfirmed that the erbium and silicon atoms occupy the 2(c) site (1/4, 1/2, 0.65) and (1/4, 1/2, 0.25), respectively, and the Ti atom occupy the special position 2(a) (0.01, 0.35, 0) and the lattice parameter are a=0.40063nm, c=0.7437nm in the ErSiTi structure. The calculated PDFs of the ErSiTi compound using the crystallographic data of Ref. [13] and this work were shown in Fig. 7, respectively. Moreover, at 773 K, the homogeneity range of Er3Si5 phase extends from about 63 at.% Si to 66 at.% Si in Er-Si system; the homogeneity range of Si3Ti5 phase extends from about 62 at.% Ti to 64 at.% Ti in Si-Ti system; the maximum solid solubility of Er in Si3Ti5 phase is about 2 at.% Er. Details of crystallographic data of the initial components and the compounds in the Er-Si-Ti ternary system are given in Table 1. TABLE1 CRYSTALLOGRAPHIC DATA OF THE INITIAL COMPONENTS AND COMPOUNDS IN THE Er–Si–Ti SYSTEM Phase
Space group
Structure type
Lattice parameter (nm) a
Er Si
P63/mmc Fd 3 m
Mg
0.3559
C
0.54309
b 0.3559
-4http://www.ivypub.org/rms
Reference c
0.5587
[18] [18]
Phase
Space group
Structure type
Lattice parameter (nm) a
Ti
P63/mmc
Mg
0.2950
Er5Si3
P63/mcm
Mn5Si3
Er5Si4 ErSi
Er3Si5 Si2Ti, SiTi,
Si4Ti5,
Pnma
Ge4Sm5
Cmcm
BCr
Pmmm
Er3Si5
Fddd
TiSi2
Pnma
FeB
P41212
Zr5Si4
Si3Ti5,
P63/mcm
Mn5Si3
SiTi3,
P42/n
Ti3P
b
c
0.2950
0.4683
[18]
0.8293
0.6220
[18]
0.8323
0.6234
This work
0.7270
1.432
0.7580
[18]
0.7148
1.4178
0.7537
This work
0.4195
1.0353
0.3779
[18]
0.4198
1.0388
0.3791
This work
0.6538
0.3793
0.4082
[18]
0.6570
0.3803
0.4076
This work
0.8236
0.4773
0.8523
[18]
0.8265
0.4803
0.8559
This work
0.6544
0.3638
0.4997
[18]
0.6553
0.3642
0.5008
This work
0.6702
—
1.2174
[8]
0.7133
1.2977
[18]
0.6766
1.2288
This work
—
0.74610
0.51508
0.7451 —
1.0196 1.0200
ErSiTi
P4/nmm
CeFeSi
—
0.40029（4）
P41212
Zr5Si4
This work
0.5097
[18]
0.5084
This work
0.74737 —
0.6964(1)
1.2776(1)
0.69619
[18]
0.5146
0.7480(1)
0.40063 Er2Si4Ti3
Reference
1.27632
[13,14] This work [15] This work
3.2 The isothermal section of the Er-Si-Ti ternary system at 773 K Er
20 Er5Si3
t% Si a
at%
5 4 6 #47 #20
80
#36
14
2 ErSiTi
40 #50
3 20
Er2Si4Ti3
7
8
#1
Si
60
#15
ErSi
Er3Si5
Er
1
40 Er5Si4 60
80
20
10 9
#8
Si2Ti 40 SiTi Ti at%
12 11
13 #10
60 Si Ti 80 3 5 Si4Ti5 SiTi
Ti
3
FIG.12 ISOTHERMAL SECTION OF Er-Si-Ti TERNARY SYSTEM AT 773 K.
By comparing and analyzing the XRD patterns of 110 samples, with the aid of optical microscopy and SEM -5http://www.ivypub.org/rms
(equipped with EDS) techniques, and identifying the phases present in each sample, the isothermal section of the phase diagram of the ternary system Er–Si–Ti was determined at 773 K. The isothermal section, shown in Fig.12, consists of 14 single-phase regions, 27 two-phase regions and 14 three-phase regions. 14 single-phase regions are: A (Er), B (Er5Si3 ), C (Er5Si4 ), D (ErSi), E (Er3Si5), F (Si), G (Si2Ti), H (SiTi), I (Si4Ti5), J (Si3Ti5), K (SiTi3), L (Ti), M (ErTiSi), and N (Er2Si4Ti3). 27 two-phase regions are: A+B, B+C, C+D, D+E, E+F, F+G, G+H, H+I, I+J, J+K, K+L, L+A, A+M, B+M, B+J, B+N, C+N, D+N, E+N, E+I, E+H, E+G, N+I, N+J, M+J, M+K and M+L. Details of three–phase regions are given in Table 2. TABLE 2 DETAILS OF THE THREE-PHASE REGIONS IN THE Er–Si–Ti TERNARY SYSTEM AT 773 K. Phase regions
Phase composition
Phase regions
Phase composition
1
Er5Si3 + ErSiTi + Er
8
Si2Ti + SiTi + Er3Si5
2
Si3Ti5 + Er5Si3 + ErSiTi
9
SiTi + Si4Ti5 +
3
Si3Ti5 + Er5Si3 + Er2Si4Ti3
10
Si4Ti5 + Si3Ti5 + Er3Si5
4
Er5Si3 + Er2Si4Ti3 + Er5Si4
11
Er2Si4Ti3 + Si3Ti5 + Si4Ti5
5
Er2Si4Ti3 + Er5Si4 + ErSi
12
Si3Ti5 + ErSiTi + SiTi3
6
Er2Si4Ti3 + ErSi + Er3Si5
13
ErSiTi + SiTi3 + Ti
7
Si + Si2Ti + Er3Si5
14
ErSiTi + Er + Ti
Er3Si5
4. Conclusion Nine binary compounds Er5Si3, Er5Si4, ErSi, Er3Si5, Si2Ti, SiTi, Si4Ti5, Si3Ti5, SiTi3 and two ternary compounds ErSiTi, Er2Si4Ti3 were confirmed in Er–Si–Ti ternary system at 773 K. At 773 K, the homogeneity range of Er3Si5 phase extends from about 63 at.% Si to 66 at.% Si in Er-Si system; the homogeneity range of Si3Ti5 phase extends from about 62 at.% Ti to 64 at.% Ti in Si-Ti system; the maximum solid solubility of Er in Si3Ti5 phase is about 2 at.% Er in Er–Si–Ti ternary system. The isothermal section of the Er-Si-Ti ternary system consists of fourteen single-phase regions, twenty-seven two-phase regions and fourteen three-phase regions.
Acknowledgements This work was jointly supported by the National Natural Science Foundation of China (50761003) and the Key Project of China Ministry of Education (207085).
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Authors 1
3
lxg213@yahoo.com.cn
tangmeng771@163.com
2*
4
supervisor. Email: gxuliujq@163.com
chunhuiliabc@yahoo.com.cn
Xueqiang Li (1973- ), male, born in Guangdong, master. Email:
Jingqi Liu (1940- ), male, born in Guangxi, professor , master's
Mengqi Tang (1983- ), male, born in Guangxi, master. Email:
Chunhui Li (1983- ), male, born in Shandong, master. Email:
-7http://www.ivypub.org/rms