|
|
Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making. |
|
Thread Tools | Display Modes |
#1
|
||||
|
||||
new steel?
I saw this on the other forum, thought you guys may be interested in reading it.
http://www.timesdispatch.com/servlet...=1045855934842 |
#2
|
|||
|
|||
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>
__________________ Stay Sharp, RJ Martin Knifemaker www.rjmartinknives.com |
#3
|
||||
|
||||
Yttrium! Dang, I knew I was supposed to pick up something else at the hardware store....
__________________ God bless Texas! Now let's secede!! |
#4
|
|||
|
|||
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 __________________ Gas Forges, Refractory, & Knifemaking Supplies Refractory.EllisCustomKnifeworks.com Visit the Forge Gallery - forge building resource pages ForgeGallery.EllisCustomKnifeworks.com |
#5
|
||||
|
||||
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!"
|
#6
|
|||
|
|||
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. __________________ Gabe Newell |
#7
|
|||
|
|||
One in a long line of breakthoughs....
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.
__________________ Which is worse; ignorance or apathy? Who knows? Who cares? |
#8
|
|||
|
|||
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 |
#9
|
|||
|
|||
__________________ Gary Hamilton |
#10
|
|||
|
|||
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 Last edited by Gabe Newell; 07-22-2004 at 12:28 AM. |
#11
|
|||
|
|||
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. Code:
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 __________________ Gabe Newell |
#12
|
|||
|
|||
TABLE II. Results obtained from DTA scan of high-manganese-boron (DARVA-Glass2) amorphous alloys.
Code:
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 __________________ Gabe Newell |
#13
|
|||
|
|||
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 |
#14
|
|||
|
|||
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 |
#15
|
|||
|
|||
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. REFERENCES 1. A. Inoue, B.L. Shen, A.R. Yavari, and A.L. Greer, J. Mater. Res. 18, 1487 (2003). 2. V. Ponnambalam, S.J. Poon, G.J. Shiflet, V.M. Keppens, R. Taylor, and G. Petculescu, Appl. Phys. Lett. 83, 1131 (2003). 3. A. Inoue, T. Zhang, and A. Takeuchi, Appl. Phys. Lett. 71, 464 (1997). 4. Z.P. Lu, C.T. Liu, and W.D. Porter, Appl. Phys. Lett. 83, 2581 (2003). 5. T. Egami and Y. Waseda, J. Non-Cryst. Solids 64, 113 (1984). 6. A. Migliori, J.L. Sarrao, W.M. Visscher, T.M. Bell, Lei Ming, Z. Fisk, and R.G. Leisure, Physica B 183, 1 (1993). 7. L.C. Chen and F. Spaepen, Nature 336, 366 (1988). 8. J.W. Christian, The Theory of Transformation in Metals and Alloys, 2nd ed. (Pergamon Press, New York, 1975). 9. Steels: Metallurgy and Applications, D. Llewellyn and R. Hudd, 3rd ed. (Butterworth-Heinemann, Boston, 1998). 10. P. Villars, A. Prince, and H. Okamoto, Handbook of Ternary Alloy Phase Diagrams (ASM International, Materials Park, OH, 1995). 11. M. Widom, D.M. Nicholson, and Y. Wang (private communications). 12. T.D. Shen and R.B. Schwarz, Appl. Phys. Lett. 75, 49 (1999). __________________ Gabe Newell |
Tags |
blade, knife |
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
|
|