Supplementary Materials:

Ductile-phase Toughening in TiBw/Ti-Ti3Al Metallic-Intermetallic Laminated Composites

HAO WU, BO CHENG JIN, LIN GENG, GUOHUA FAN, XIPING CUI, MENG HUANG, RODRIGO MIER HICKS, and STEVEN NUTT

HAO WU, Ph.D. Student, LIN GENG,Professor,GUOHUA FAN, AssociateProfessor,XIPING CUI, Ph.D., and MENG HUANG, Master Student, are with School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, P.R.China. Contact e-mail: . BO CHENG JIN,Ph.D. Student, RODRIGO MIER HICKS, Master Student, and STEVEN NUTT, Professor, are with M.C. Gill Composites Center, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-0241, U.S.A.

Part A: Synthesis process during reaction annealing

The synthesis of the TiBw/Ti-Ti3Al MIL composite is a two-step process. First, during the initial annealing at 943 K (670 °C), the nucleation of TiAl3 is expected to occur at the interface between the TiBw/Ti(s) and Al(l) layers. The reaction rate decreases progressively with increasing annealing time due to the progressively thicker barrier to diffusion caused by the newly-formed TiAl3 layer.[1] Thus, the next reaction process depends on the interdiffusion of Ti and Al, which is driven by the sustaining concentration gradients of Ti and Al within different phases (Fig. S1a). As this process proceeds, the TiAl3 layer continually thickens until the Al has been completely consumed (Fig. S1b). However, voids are formed in the Al layer as a consequence of the difference in the diffusion rates of Ti and Al (the Kirkendall effect),[2, 3] although the voids are eliminated by subsequent densification (Fig. S1b). The newly-formed TiAl3 phase transforms to TiAl and Ti3Al at 1473 K (1200 °C) due to the elemental interdiffusion in the solid-solid reaction (Fig. S1c). Finally,laminated composites comprised of alternating TiBw/Ti and Ti3Al layers are obtained (Fig. S1d).

The TiBwreinforcement is migrated towards the TiBw/Ti centerline due to a higher diffusion rate of Al to Ti.The volume fraction of TiBw in the TiBw/Ti layer increases from 5% (Fig. 1a) to 17% (Fig. 2b). Numerous TiBw significantly refines the TiBw/Ti grains depending on the phase transformation β-Ti →α-Ti at 1155 K (882°C) during the furnace cooling stage.

Fig. S1.Schematic of the synthesis of TiBw/Ti-Ti3Al MIL composites. (a) First stage, showing the interdiffusion of Ti and Al in solid TiBw/Ti and liquid Al during the initial annealing at 943 K (670 °C). (b) Second stage, showing the composite after initial annealing, consisting of newly-formed TiAl3 layers and unreacted TiBw/Ti layers. (c) Third stage, showing the phase transformation within Ti-Al intermetallic compounds during the densification treatment at 1473 K (1200 °C). (d) Fourth stage, showing the layered microstructure of the MIL composite comprised of TiBw/Ti and Ti3Al layers.

Part B: Simulation

1. Basic parameters

The parameters used in the simulation are listed in below Table 1.

Table 1. Basic parameters at room temperature

Ti3Al / Ti
ρ (g/cm3) / 4.2 / 4.54
ν / 0.29 [4] / 0.32 [5]
E (GPa) / 148[4] / 117 [5]
G (GPa) / - / 44 [5]
σs (MPa) / 599 [4] / 393 [6]
Elongation (%) / 0.3 / 20.7 [6]

2. Material systems

Material system informationof Ti-Ti3Al laminated composites and monolithic Ti3Al are listed in Tables 2 and 3, respectively.

Table 2. Ti-Ti3Al laminated composites

Ti3Al / Ti
Single layer thickness (μm) / 300 / 150
Layer number / 5 / 4

Table 3. Monolithic Ti3Al

Ti3Al / Ti3Al
Single layer thickness (μm) / 300 / 150
Layer number / 5 / 4

3. FEA model

The model was set up according to ASTM E1820 which is an international standard (SI). And the simulation we performed is only within linear regime to compare and evaluate the mechanical properties of the material systems. The model and the coordinate system used are shown in Fig. S2. This 3D model consists of several rectangular prisms stacked together to represent the different layers of materials. 3D solid elements were used in meshing and were arranged in an assembly that matches the material system’s layout definition. Tie constraints were used between interfaces.

Fig. S2. A 3D FEA model (ABAQUS).

4. Geometricparameters

The ASTM recommended specimen geometric configurations were used and shown in Fig. S3.

Fig. S3. Geometric configurations of the model (ABAQUS).

5. Boundary and loading conditions

The boundary and loading conditions of the model are shown in Fig. S4. The translation in z axis (axis coordinates shown in Fig. S2) is fixed as T3=0. The indenter pins are restrained to move only in Y direction. Frictionless contact condition was applied between the three indenter pins and the specimen body.

Fig. S4. The boundary and loading conditions of the model.

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