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Bulk metallic glasses (BMGs ) have displayed impressive mechanical properties , but
the use and dimensions of material have been limited due to critical cooling rate
requirements and low ductility . The application of severe plastic deformation by equal
channel angular extrusion (ECAE ) for consolidation of bulk amorphous metals (BAM )
and amorphous metal matrix composites (AMMC ) is investigated in this dissertation .
The objectives of this research are a ) to better understand processing parameters which
promote bonding between particles and b ) to determine by what mechanisms the
plasticity is enhanced in bulk amorphous metal matrix composites consolidated by
ECAE .
To accomplish the objectives BAM and AMMCs were produced via ECAE
consolidation of Vitreloy 106a (Zr58 .5Nb2 .8Cu15 .6Ni12 .8Al10 .3 -wt % ) , ARLloy #1
(Hf71 .3Cu16 .2Ni7 .6Ti2 .2Al2 .6 -wt % ) , and both of these amorphous alloys blended with
crystalline phases of W , Cu and Ni . Novel instrumented extrusions and a host of postprocessing
material characterizations were used to evaluate processing conditions and
material properties . The results show that ECAE consolidation at temperatures within the supercooled liquid region gives near fully dense ( >99 % ) and well bonded millimeter
scale BAM and AMMCs . The mechanical properties of the ECAE processed BMG are
comparable to cast material : à  f = 1640 MPa , à µf = 2 .3 % , E = 80 GPa for consolidated
Vitreloy 106a as compared to à  f = 1800 MPa , à µf = 2 .5 % , E = 85 GPa for cast Vitreloy
106 , and à  f = 1660 MPa , à µf = 2 .0 % , E = 97 GPa for ARLloy #1 as compared to à  f = 2150
MPa , à µf < 2 .5 % , E = 102 GPa for Hf52Cu17 .9Ni14 .6Ti5Al10 . The mechanical properties of
AMMCs are substandard compared to those obtained from melt -infiltrated composites
due to non -ideal particle bonding conditions such as surface oxides and crystalline phase
morphology and chemistry . It is demonstrated that the addition of a dispersed crystalline
phase to an amorphous matrix by ECAE powder consolidation increases the plasticity of
the amorphous matrix by providing locations for generation and /or arrest of adiabatic
shear bands . The ability of ECAE to consolidated BAM and AMMCs with improved
plasticity opens the possibility of overcoming the size and plasticity limitations of the
monolithic bulk metallic glasses . |
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