new steel?

[rhrocker]

I saw this on the other forum, thought you guys may be interested in reading it.
http://www.timesdispatch.com/servlet...=1045855934842

[RJ Martin]

Robert: Thanks for posting that-It's interesting stuff. I knew that big pile of Yttrium I have in my back yard would be useful some day........<G>

[TexasJack]

Yttrium! Dang, I knew I was supposed to pick up something else at the hardware store....

[Darren Ellis]

Oh my gosh, I know Joe Poon from back in the days when I was working at UVA's physics department on some nuclear physics research for CEBAF! How cool, he's now working on some things that I'm interested in!

-Darren

[Don Halter]

Interesting! Yttrium is one of the rare earth samples I have that I was going to play with when I start messing with crucible steels. Any idea how well it would form carbides? I have some niobium and tantalum as well. I put a list a while back on the outpost of the assortment I had. New headlines: "Home foundry turned liquid steel production center!"

[Gabe Newell]

This is an update to Liquid Metal, correct? I thought the bottom line on Liquid Metal was that unless you were taking advantage of it's micron level castability (which could be super cool), that it wasn't that interesting a blade material. It isn't very hard, and doesn't have great impact strength (charpy-c). It had neat acoustic properties, but I don't think you want to go out of your way to make a knife that bounces really well.

Dr. Poon can be reached at 434-924-6792 or sjp9x@virginia.edu. I'll send him an email.

[Quenchcrack]

I have been a member of the American Society for Metals and Materials for about 30 years now. I get their magazine every month. Once or twice per year I have read about a "fantastic breakthough that will replace steel, revolutionize the metals industry, and cure zits". I have usually never heard of them again. I hope this one lives up to the promotions.

[Gary Hamilton]

Ok I may need more help from smart people on this, my understanding was similar to Gabes comments. It sound like liquid metal which I believe is also an amorphous alloy. One item I seemed to remember related to liquid metal was that it developed a grain structure after aging. I won't swear on anything but I do have a few links saved on it.

[Gary Hamilton]

[Gabe Newell]

I heard back from Dr. Poon. He sent me two papers he had published. I can email people the PDF files which are much more legible than cutting and pasting the text:

Synthesis of iron-based bulk metallic glasses as nonferromagnetic amorphous steel alloys

V. Ponnambalam and S. Joseph Poona
Department of Physics, University of Virginia, Charlottesville, Virginia 22904-4714

Gary J. Shiflet
Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904-4745

Veerle M. Keppens, R. Taylor, and G. Petculescu
Department of Physics, The University of Mississippi, National Center for Physical Acoustics, Coliseum Drive, University, Mississippi 38677

(Received 25 November 2002; accepted 10 June 2003)

Iron-based amorphous metals are investigated as nonferromagnetic amorphous steel alloys with magnetic transition temperatures well below ambient temperatures. Rod-shaped amorphous samples with diameters reaching 4 mm are obtained using injection casting. Amorphous steel alloys are designed by considering atomistic factors that enhance the stability of the amorphous phase, coupled with the realization of low-lying liquidus temperatures. The present alloys are found to exhibit superior mechanical strengths. In particular, the elastic moduli are comparable to those reported for super austenitic steels. ? 2003 American Institute of Physics. [DOI: 10.1063/1.1599636]

To date, bulk-solidifying iron-based amorphous metallic alloys are used mainly for soft-magnetic applications.1?3 These amorphous metals also exhibit specific strengths and Vickers hardness two to three times those of high-strength steel alloys; in some cases, good corrosion-resistant properties have been reported.4 Bulk samples of these amorphous metals are usually prepared as rods 1?3 mm in diameter by injection casting. It has also been shown that amorphous rods 4 mm in diameter can be obtained by fluxing Fe-alloy powders followed by quenching the alloy melt in water.2 The good formability of Fe-based amorphous metals are attributed to the high reduced glass transition temperature Trg (glass temperature Tg divided by liquidus temperature Tl in K) of ~0.6? 0.63 and large supercooled liquid region DTx (crystallization temperature minus glass transition temperature) of at least ~30 ?C measured. Clearly, it is also an attractive idea to develop Fe-based bulk amorphous metals as nonferromagnetic steel alloys.

We report in this letter amorphous steel alloys that exhibit magnetic transition temperatures significantly below room temperature. The alloy synthesis strategy will involve achieving high glass formability as well as suppressing ferromagnetism. Recent atomistic modeling and theoretical efforts have led to some insights on glass formability that are unknown from the empirical rules. The latter state that the alloys must be multicomponent, the heats of formation between the components must be negative, and the atomic sizes must be sufficiently different.1,2 The new studies have revealed some specific connections between atom size, interaction, and alloy composition which are found to favor a high Tg .5?7 The latter findings will be combined with the low magnetic temperature and low Tl requirements to meet the following desired objectives for designing nonferromagnetic amorphous steel alloys:

(i) Suppressing magnetic effect. Mn is used in suppressing ferromagnetism;8 Cr is also added, but in a much smaller amount in view of point (ii).

(ii) Decreasing Tl to obtain high Trg . For Fe-based alloys, the inclusion of metalloids is necessarily to achieve a low Tl . Additions of Mn and some refractory metals, such as Zr, Nb, and Mo, but not Cr, can further depress Tl by various magnitudes.

(iii) Increasing Tg . Refractory metals are added to enhance Tg through increase in the elastic moduli9 as well as enhancement in the stability of the amorphous structure. According to a recently proposed structure-reinforcement model,7 the more strongly associated refractory metal?metalloid minority atom groups are said to form a backbone structure which increases the viscosity of the melt, thus adding to the glass formability.

(iv) Constituting alloy composition. Preferable compositions for efficient packing in amorphous metals has been proposed.5 For elemental components with the three primary atom sizes considered, which include Fe (Mn) atoms, small metalloid atoms, and large refractory metal atoms, the optimal large-atom content is estimated to be ;10 at. %. Such atom size distribution will further reinforce the amorphous structure because the atoms in the backbone, with the large refractory atoms having a high coordination number and the small metalloid atoms occupying the interstitial sites, can interact effectively with the majority Fe atoms.

It is clear from the previous discussion that the selection of elemental components and their relative compositions must be considered simultaneously. Thus, in order to optimize glass formability, the constitution of alloy composition discussed in point (iv) must also take into account points (ii) and (iii). An initial test of our synthesis approach is performed by first studying several ternary Fe?Zr?B and quaternary Fe?Mo?(C,B) alloys. Other ternary alloys, such as Fe?Zr?C and Fe?Mo?B, are not pursued in view of the high Tl>1200 ?C measured. Significant enhancement in the glass formability is found when ;10 at. % Zr and 14 at.% Mo are added to Fe?B and Fe?(C,B) alloys, respectively, as evident in the large increase in Tg of ~150 ?C in these alloys (e.g., In Fe80B20 , Tg is unclear, but below Tx(5430 ?C); in Fe78C15B7 , Tg5350 ?C, Trg;0.43). As a result, Trg is increased from ~0.43 in Fe78C15B7 to 0.59 in Fe64Mo14C15B7. The latter Trg value is sufficiently high for casting bulk amorphous samples (Table I). In fact, the present Fe?Mo?C?B alloys are the only quaternary Fe-based alloys reported to date that can form up to 2.5-mm-diameter amorphous rods. The latter findings differ significantly from those reported for similar quaternary Fe-based alloys formed at a different composition, which can only yield up to 1-mm-diameter amorphous rods.4 On the other hand, for Fe70Zr10B20 which has a rather high Tl despite its high Tg of 570 ?C, further substitution of Fe with Mn is found necessary to bring about a large reduction in its Tl , by as much as 100 ?C, in order to increase Trg from 0.55 to 0.58 (Table II).

Alloy ingots used in the present study were prepared by melting nominal amounts of high-purity elements in an arc furnace under an argon atmosphere. Bulk-solidifying samples were prepared by injecting the melt into the cylinder-shaped cavity inside a copper block. For most of the ~Fe,Mn,Cr!?~Zr,Nb!?B alloys investigated, amorphous ribbons were made by melt-spinning technique under a partial helium atmosphere. The amorphous nature of the samples was verified with an x-ray diffractometer. Some samples were further examined in a transmission electron microscope. Thermal analysis was performed using a differential thermal analyzer (DTA) at a heating rate of 10 ?C/min. Magnetic measurements were carried out using a Quantum Design magnetic property measurement system. Magnetic transition was determined using an applied field of 100 Oe. Magnetization measurement at 5 K was extended to higher fields up to 4 T. Hardness measurements were made using a Vickers microhardness tester. Tensile testing of melt-spun ribbons was done using a servohydraulic testing machine. Elastic moduli were determined by employing the resonant ultrasound spectroscopy technique developed by Migliori et al.10 An amorphous sample has two elastic moduli, a shear modulus C44 and a compressional modulus C11 . The measurements reported in this letter were performed on 3-mmdiameter amorphous (Fe,Mn,Cr)?Mo?(C,B) alloy specimens each cut into a rectangular parallelepiped with dimensions 2.932.131.9 mm3.

Two groups of Fe-based amorphous metals are investigated for their glass formability. One group of alloys contains manganese, molybdenum, and carbon as the principal alloying components with Fe. These high-manganese?molybdenum?carbon alloys are called DARPA-University of Virginia-Glass1 (DARVA-Glass1) alloys. The other group contains manganese and boron as the principal alloying components with Fe. These high-manganese?boron alloys are called DARVA-Glass2 alloys. Most of the DARVA-Glass1 alloys investigated are found to exhibit Trg~0.6 and DTx ~45? 55 ?C. Several typical DARVA-Glass1 alloys are listed in Table I. The alloys exhibit similar Tl values. Despite the moderate Trg and DTx exhibited by these alloys, amorphous rods of up to 4 mm in diameter and several centimeters in length can be readily produced using injection casting. A camera photo of six injection-cast amorphous rods is displayed in Fig. 1. DTA scans obtained from two bulk amorphous samples of composition e50Mn10Mo14Cr4C16B6 are shown in Fig. 2. The x-ray diffraction (XRD) and electron diffraction (ED) patterns from a 4-mm-diameter rod of composition Fe51Mn10Mo14Cr4C16B5 , which are characteristic of that of an amorphous phase, are shown in Fig. 3. The DTA scan of the latter sample shows the same Tg , DTx , and Trg values as those seen in Fig. 2.

(continued next post)

[Gabe Newell]

Table 1

TABLE I. Typical high-manganese?molybdenum?carbon (DARVA-Glass1) amorphous alloy compositions and the maximum diameters of the bulksolidifying amorphous rods obtained. Most of the alloys have similar Tg ~530?550?C, DTx~45? 55?C, Tl~1080?1090?C, Trg~0.60?0.61, except for Fe64Mo14C15B7, which has the corresponding values 520?C, 50?C, 1070?C, and 0.59.

Fe64Mo14C15B7                2.5 mm
Fe54Mn10Mo14C15B7            3 mm
Fe50Mn10Mo14Cr4C15B7         3 mm
Fe50Mn10Mo14Cr4C16B6         4 mm
Fe49Mn10Mo14Cr4W1C16B6       4 mm
Fe51Mn10Mo14Cr4C15B6         4 mm
Fe48Mn10Mo16Cr4C15B7         3 mm
Fe50Mn10Mo14Cr4C15B7         3 mm
Fe49Mn10Mo14Cr4W1C15B7       3 mm
Fe48Mn10Mo13Cr4W3C15B7       2 mm
Fe49Mn10Mo13Cr3W3C15B7       2 mm
Fe46Mn10Mo16Cr4Ga2C15B7      2 mm
Fe49Mn10Mo14Cr4V1C15B7       3 mm

(continued next post)

[Gabe Newell]

TABLE II. Results obtained from DTA scan of high-manganese-boron (DARVA-Glass2) amorphous alloys.

Alloy                           Tg(?C)     DTx(?C)    Tl(?C)    Trg
 Fe68Zr10B22                     570          70       1260    0.55
(Fe0.75Mn0.25)70Zr9B21           560          70       1163    0.58
(Fe0.70Mn0.25Cr0.05)68Zr7Nb3B22  613          78       1170    0.61
(Fe0.69Mn0.26Cr0.05)68Zr10B19C3  580          70       1150    0.60
(Fe0.69Mn0.26Cr0.05)70Zr4Nb4B22  595          78       1127    0.62
(Fe0.69Mn0.26Cr0.05)68Zr6Nb2B24  591          78       1140    0.61
(Fe0.69Mn0.26Cr0.05)68Zr4Nb4B24  613          85       1140    0.63
(Fe0.70Mn0.30)65Zr4Nb4Mo3B24     605          87       1120    0.63

(continued next post)

[Gabe Newell]

A number of melt-spun DARVA-Glass2 alloys and their
Tg , DTx , Tl , and Trg values are given in Table II. The DTA
scans for several of these alloys have been published
elsewhere.7 These alloys are found to exhibit Trg ranging
from 0.59 to a high value of ;0.63 and DTx from 60 ?C to
more than 80 ?C. The amorphicity of these alloys are con-
firmed by XRD. Given the favorable glass forming parameters,
it is expected that some of these alloys can be easily
processed into bulk amorphous samples with a thickness of
several millimeters. Because of the high melt viscosity observed,
the melt must be heated to temperatures considerably
higher than Tl in order to carry out injection casting. As a
result, the effectiveness in heat removal is significantly reduced,
and only the (Fe0.69Mn0.26Cr0.05)68Zr4Nb4B24 and
(Fe0.66Mn0.29Mo0.05)68Zr4Nb4B24 alloys can be cast into
amorphous rods of 2 mm in diameter.
The two alloy groups are found to exhibit magnetic transitions
at temperatures significantly below the ambient temperature.
For example, (Fe0.69Mn0.26Cr0.05)68Zr4Nb4B24 is
ferromagnetic below 160 K and Fe51Mn10Mo13Cr4C15B7 exhibits
a spin-glass-like transition at 15 K. For the former
alloy, the saturation moment is estimated to be 0.56 mB per
atom at 5 K, while for the latter alloy, an effective moment of
1.62 mB per atom is obtained, which yields a total angular
momentum J50.45 per atom for a g-factor of 2. Thus, the
magnetic moments are much smaller than those reported for
ferromagnetic Fe-based amorphous metals.1,2 The small
magnetic moments measured in the present alloys are in
good agreement with predictions from recent ab initio
calculations.11 The overall magnetic moment reduction is due
to canting of the iron moments as well as the presence of
antiferromagnetic coupling due to alloying. Preliminary
hardness measurements show Vickers hardness in the range
of 1200 to 1500 DPN for both the DARVA-Glass1 and
Glass2 alloys. Using these values, a tensile strength of
;4000 MPa is estimated.12 Unfortunately, the bulk samples
used in our compression and tensile tests tend to crack prematurely
at values of ;1000 MPa. The latter is attributed to
the porosity of the amorphous rods noted. On the other hand,
very high tensile fracture strengths of ;3000 MPa are measured
in the DARVA-Glass1 alloy ribbons. Meanwhile, unexpectedly
low tensile fracture strengths spanning a wide
range of ;400 to 1000 MPa are found in the DARVA-Glass2
alloy ribbons. The low values measured on the latter samples
can be attributed to the brittleness of the DARVA-Glass2
alloy ribbons. Due to the high melt viscosity of the Mn?B
alloys, such embrittlement is likely the result of an annealing
effect caused by the high temperature needed in producing
the ribbon samples. The elastic constants C11 and C44 measured
on two 3-mm-diameter amorphous rods of the
Fe50Mn10Mo14Cr4C15B7 alloy give the averaged values of
296 and 80 GPa, respectively. Measurements made on the
two samples differ by ;3%. Based on the C11 and C44
values obtained, the Young?s modulus and bulk modulus are
found to be 210 and 190 GPa, respectively.
The work at the University of Virginia is supported by
the DARPA Structural Amorphous Metals Program in the
form of ONR Grant N00014-01-1-0961. The work at The
University of Mississippi is supported by an ONR Grant.
1 A. Inoue, T. Zhang, H. Yoshiba, and T. Itoi, Mater. Res. Soc. Symp. Proc.
554, 251 ~1999!.
2T. D. Shen and R. B. Schwarz, Appl. Phys. Lett. 75, 49 ~1999!.
3 A. Inoue, A. Takeuchi, and B. Shen, Mater. Trans., JIM 42, 970 ~2001!.
4 S. Pang, T. Zhang, K. Asami, and A. Inoue, J. Mater. Res. 17, 701 ~2002!.
5 O. N. Senkov and D. B. Miracle, Mater. Res. Bull. 36, 2183 ~2001!.
6T. Egami, Mater. Trans., JIM 43, 510 ~2002!.
7 S. J. Poon, G. J. Shiflet, F. Q. Guo, and V. Ponnambalam, J. Non-Cryst.
Solids 317, 1 ~2003!.
8 O. Beckmann, K. Gramm, L. Lundgren, P. Svedlindh, K. V. Rao, and H. S.
Chen, Phys. Scr. 25, 676 ~1982!.
9T. Egami, Mater. Sci. Eng., A 226?228, 261 ~1997!.
10 A. Migliori, J. L. Sarrao, W. M. Visscher, T. M. Bell, Lei Ming, Z. Fisk,
and R. G. Leisure, Physica B 183, 1 ~1993!.
11 D. M. Nicholson, Y. Wang, and M. Widom ~private communication!.
12 H. S. Chen, Rep. Prog. Phys. 43, 2350 ~1980!.

[Gabe Newell]

Fe-based bulk metallic glasses with diameter thickness larger
than one centimeter

V. Ponnambalam and S. Joseph Poona
Department of Physics, University of Virginia, Charlottesville, Virginia 22904-4714

Gary J. Shiflet
Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904-4745

(Received 15 December 2003; accepted 17 February 2004)

Fe?Cr?Mo?(Y,Ln)?C?B bulk metallic glasses (Ln are lanthanides) with maximum
diameter thicknesses reaching 12 mm have been obtained by casting. The high glass
formability is attained despite a low reduced glass transition temperature of 0.58. The
inclusion of Y/Ln is motivated by the idea that elements with large atomic sizes can
destabilize the competing crystalline phase, enabling the amorphous phase to be
formed. It is found that the role of Y/Ln as a fluxing agent is relatively small in terms
of glass formability enhancement. The obtained bulk metallic glasses are
non-ferromagnetic and exhibit high elastic moduli of approximately 180?200 GPa and
microhardness of approximately 13 GPa.

Iron-based bulk metallic glasses have been reported to
exhibit high yield strengths two to three times those of
high-strength steels and elastic moduli comparable to
those of super-austenitic steel alloys.1,2 These bulk metallic
glasses alloys are beginning to gain recognition as
a new class of structural materials with certain superior
properties, such as strength. In particular, bulk amorphous
Fe?Mn?Cr?Mo?C?B alloys, which can be cast
into 4 mm-diameter rod-shaped samples, are called nonferromagnetic
amorphous steel alloys.2 To date, the most
formable Fe-based bulk metallic glasses are reported to
form 5 to 6-mm-diameter samples.3,4 Because of the ability
to process them is limited, the potential for Fe-based
bulk metallic glasses as structural materials has yet to be
realized.
In this paper we report a significant increase in the
formability of Fe?Cr?Mo?C?B bulk metallic glasses
when alloyed with few atomic volume fractions of Y and
Ln (lanthanides). The improvement on glass formability
upon adding Y/Ln is realized. The maximum attainable
diameter of glassy Fe50Cr15Mo14C15B6 samples is
only 1.5 mm, but is increased to 9?12 mm with only
2 at.% Y/Ln addition. Although the study focused mainly
on the Er-containing alloys, additions of other Ln such as
Dy, Yb, and Gd produce essentially similar results. Preliminary
measurements of mechanical and magnetic
properties are also reported. While it has recently been
shown that the glass formability of Fe?Co?Mo?Zr?B alloys
can be improved by adding 2 at.% Y,4 the idea of
adding Y/Ln to Fe?Mn?Cr?Mo?C?B alloys has been independently
pursued by our group. The key results presented
herein were reported in a program review conducted
by DARPA in February 2003; a patent disclosure
on our alloys was filed by the University of Virginia
Patent Foundation in April 2003. The utilization of Y/Ln
to enhance the glass formability is motivated by the idea
that if the atomic-level stress due to large atom solutes
has become too large for the crystalline state to remain
stable, the system will be left in the vitrified state upon
cooling from the melt.5 The Y/Ln to Fe atomic size ratios
of approximately 1.4 are practically the largest values
attainable in Fe-based alloys. Since Fe?Cr?Mo?C?B is
found to devitrify into a single crystalline phase, the present
alloy provides an ideal system for applying the idea
of vitrification via destabilization of the crystalline state.
In this work, the roles of Y/Ln on glass formability are
investigated.
Alloy ingots were prepared by melting appropriate
amounts of Fe (99.9%), Cr (99.99%), Mo (99.9%), Y/Ln
(99.9%), C (99.99%), and B (99.9%) in an arc furnace
under an argon gas. The total weight loss due to melting
was found to be less than 0.2% of the starting materials.
Samples were prepared by injecting the molten alloys
contained in a quartz tube into the cylinder-shaped cavity
of a copper mold. The prepared samples were sectioned
and metallographically examined, using an optical
microscope to explore the inhomogeneity across the
fractured surface. Using a Scintag x-ray diffractometer
and copper target, x-ray diffraction (XRD) was
performed to examine the amorphicity of the inner parts
of the samples. Thermal studies were performed using
differential thermal analysis (DTA) and differential scanning
calorimetry (DSC) techniques. The heating rate applied
was 10 ?C per minute. Oxygen contents in the
samples were analyzed at Wah Chang, an Allegheny
Technologies company. Samples were fused with graphite
crucibles in an impulse-type fusion furnace heated to
approximately 3000 ?C, followed by infrared detection of
carbon dioxide. Preliminary measurements of mechanical
and magnetic properties were performed. The nonferromagnetic
nature of the samples was tested with a
strong bar magnet. Magnetic transitions of some samples
were detected by using a Quantum Design magnetic
property measurement system. Elastic moduli were determined
by employing the resonant ultrasound spectroscopy
technique.6 The ultrasound spectroscope was manufactured
by Quasar International. Measurements were
performed on rectangular parallelepiped with dimensions
2.0 ? 3.0 ? 3.5 mm3. Hardness measurements were made
using a Vickers microhardness tester.
The XRD obtained for a 10-mm-diameter sample is
shown in Fig. 1. Similar patterns that indicate amorphicity
of the samples are also obtained for the 9-mm
and 12-mm-diameter rods. A camera photo of two
glassy rods of 10 mm and 12 mm in diameter is shown
in the inset of the figure. The fractured segment of a
12 mm-diameter sample is also included in the photo. A
shiny appearance typical of a bulk glassy alloy can be
seen on the fractured surface. In casting the samples with
large diameters, the casting conditions must be optimized
to achieve a more uniform flow so that a large size
whole-piece product can be obtained. In addition to the
XRD, isothermal DSC experiments are also performed in
the supercooled liquid region. The isothermal transformation
curves obtained for glassy Fe48Cr15Mo14Er2C15B6
shown in Fig. 2 follow those expected in a truly amorphous
phase that crystallizes via a nucleation-and-growth
process.7 This analysis is based on the Johnson?Mehl?
Avrami transformation theory8 in which an effective activation
energy for the nucleation-and-growth process is
obtained as approximately 400 kJ/mol, or about 4.2 eV.
The alloys exhibit non-eutectic melting with a liquidus
region of 70?90 ?C, as shown in Fig. 3. Results obtained
from several typical alloys are listed in Table I. The
supercooled liquid regions are only approximately 40 ?C,
and the changes in glass transition temperature Tg and
crystallization temperature Tx resulting from Y/Ln additions
are small. Despite the decrease in liquidus temperature,
Tl of up to 30 ?C, given the high Tl, the reduced
glass transition temperature Trg increases only from 0.57
in Fe50Cr15Mo14C15B6 to 0.58 in the large size amorphous
samples.
Some preliminary measurements of properties are that
the alloys exhibit a spin-glass-like magnetic transition at
approximately 30 K. The elastic constants of glassy alloys
of composition Fe48Cr15Mo14Er2C15B6 and similar
glassy alloys but with slightly different Mo and Y/Ln
contents exhibit basically similar compressional modulus
C11 and shear modulus C44 values of approximately 280
and approximately 75 GPa, respectively. Measurements
made on different samples differ by less than approximately
5%. The Young?s and bulk moduli are found to be
approximately 200 GPa and about 180 GPa, respectively.
The bulk modulus is approaching that of super-austenitic
steel.9 The microhardness of these alloys are typically in
the range 1200?1300 DPN, based on which a tensile
strength of approximately 4 GPa can be estimated.1
Comparing with those alloys that do not contain Y/Ln,
it is suggested that the remarkable enhancement in glass
formability observed cannot be attributed to the relatively
low Trg ∼ 0.58. If a different parameter Tx/(Tg + Tl)
were used,4 the reduced temperature value would be approximately
0.39. In comparison, previous reports of
5-mm-diameter amorphous iron alloys showed appreciably
higher Trg ∼ 0.61 to 0.62 and Tx/(Tg + Tl) ∼ 0.41.3,4
Further studies will be needed to fully understand the
significant enhancement in glass formability despite the
moderate Trg value. One plausible mechanism is that the
competing single metastable Fe23C6 phase10 that forms
upon the devitrification of Fe?Cr?Mo?C?B becomes less
stable when alloyed with Y/Ln, as found in recent cohesive
energy calculations.11 Meanwhile, it is observed that
upon alloying with Y/Ln, the growth of Fe23C6 phase
during devitirification is drastically impeded. These findings
taken in sum suggest that while the large atoms can
be accommodated in the melt, their presences in the crystalline
structure decrease the stability of the Fe23C6

[Gabe Newell]

metastable phase relative to the amorphous structure. As
a result, larger bulk metallic Fe-based glassy samples can
be formed even without an enhanced Trg.
Finally, the extrinsic effect of Y/Ln on glass formability
is considered. It has recently been suggested that elemental
Y played the role of oxygen scavenger in some
glassy Fe-alloys, which led to the suppression of heterogeneous
nucleation and improved glass formability.4
Earlier, it was shown that the formability of some
Fe-based bulk amorphous alloys could be improved by
fluxing the alloy powders prior to forming a molten ingot.
12 To evaluate the extent of similar extrinsic effects
in our alloys, we have studied the formability of bulk
glassy samples both as a function of Er content and oxygen
content. Formability is represented by the largest
amorphous sample diameter attainable at each Er concentration;
and oxygen is presumed to be present either in
the form of oxide or solid solution. Figure 4 shows plots
of critical sample diameter and oxygen content of
injection-cast amorphous samples as a function of Er
content. Measurements were repeated on two of the compositions.
In addition, the oxygen content of a sample
with 2 at.% Y in place of Er is found to be similar to that
of the Er-containing sample. Overall, the oxygen
levels detected in the present glassy alloys are found
to be approximately 150?300 ppm, which are about
an order of magnitude lower than those found in the
FeB-type alloys.4 It is likely that molten carbide in these
high-carbon alloys acts as the major fluxing agent, which
effectively eliminates most of the oxygen inclusion during
the melting process. In view of the low oxygen contents
measured, the present investigation indicates an intrinsic
role, rather than extrinsic role, played by Y/Ln
in the remarkable enhancement of glass formability
observed.
In summary, non-ferromagnetic bulk metallic Fe-based
glassy alloys with maximum diameter thicknesses of 1 cm
or larger have been obtained by the injection casting technique.
The remarkable enhancement in glass formability
achieved, with sample thickness increasing from 1.5 mm to
1.2 cm, using large size Y and Lanthanide atoms is discussed
in light of destabilization of the competing crystalline
phase. It is found that any positive contribution to
glass formability by Y/Ln acting as a fluxing agent is
probably small. High elastic moduli of approximately
180?200 GPa and microhardness of ∼13 GPa have also
been measured.
ACKNOWLEDGMENT
The research is supported by the DARPA Structural
Amorphous Metals Program under ONR Grant No.
N00014-01-1-0961.

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