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Development of Mo composites based on the Mo-Si-B system has been demonstrated as a possible new route to achieving a high temperature Mobased material. In this new system, the silicide phases are replaced directly with silica or other silicate materials. These composites avoid the high ductile to brittle transition temperature observed for Mo-Si-B alloys by removing the Si that exists in solid solution in Mo at equilibrium with its silicides. A variety of compositions is tested for room temperature ductility and oxidation resistance. A system based upon Mo, Mo2B, and SrO·Al2O3·(SiO2)2 is shown to possess both ductility at 80 vol.% Mo and oxidation resistance at 60 vol.%. These composites can be produced using a powder processing approach and fired to greater than 95% theoretical density with a desirable microstructure of isolated boride and silicate phases within a ductile Mo matrix.

Investigations of the production of thin-walled steel alloys through the gas carburization of structures made from reduced and sintered metal oxide powders were performed. Extrusions with low-alloy steel composition were produced successfully without the occurrence of metal dusting, yielding a novel technique for the production of thin-walled steel structures. Thin strip geometries (~200 to 300 μm final thickness) of samples with the composition of 4140 steel, without carbon, were produced through the extrusion of a paste of metal-oxide powders. Full reduction and sintering in a 10 pct H2/90 pct Ar atmosphere yielded a metal part containing all necessary alloying elements except carbon. Gas carburization in a controlled CO/CO2 atmosphere was then used to introduce carbon through the thickness of the structure while carburization parameters were controlled such that metal dusting was not observed. It has been shown in this study, through heat treatment and microstructural investigations, that structures with 4140 composition displaying microstructures and mechanical properties comparable with conventionally made steels can be reached in approximately 30 minutes during gas carburization. The research shows that carbon contents above the eutectoid composition can be reached in less than 30 minutes. As a result, a novel alloy development tool has been introduced.

Mo-Si-B alloys are candidate materials for next-generation jet engine turbine blades and have the potential to increase the service temperature of the base metals 200°C higher than nickel superalloys. These refractory alloys form a composite microstructure of molybdenum solid Solution (Moss and two intermetallic phases, Mo3Bi and Mo5SiB2, where the Moss phase enhances toughness and the intermetallic phases provide oxidation resistance. The properties of the alloys are highly dependent on the morphology of the microstructure. A powder processing approach has been developed to synthesize the three-phase alloys through the reaction of molybdenum, Si3N4 and BN powders. Electron backscatter diffraction imaging has been used to map the location of individual phases and provide a method for quantifying the Cluster size distribution of a secondary phase to examine the effect of BN reactant powders on the dispersion of the intermetallic phases.

Cellular materials, metallic bodies with gaseous voids interspersed throughout the solid body, are a promising class of materials that offer high strength accompanied by a relatively low mass. Recent research has focused in the topological design of cellular materials in order to satisfy multiple design objectives. Unfortunately, these design advances have not been met with similar advances in cellular material manufacturing as existing techniques constrain a designer to a predetermined part mesostructure, material type, and macrostructure. In an effort to address these limitations, the authors have developed a manufacturing process chain centered on an augmented three-dimensional printing process. Specifically, metallic cellular materials are made by selectively printing solvent into a bed of spray-dried metal oxide ceramic powder. The resulting green part is then sintered in a reducing atmosphere to chemically convert it to metal. The resultant process has produced maraging steel cellular artifacts featuring a 270-μm wall thickness and angled trusses and channels that are less than 1 mm in diameter.

Mo-Si-B intermetallic alloys have the potential to possess the oxidation resistance and mechanical properties required for the next generation of jet turbine engine blades. In a novel approach, three-phase alloys of α-Mo, Mo3Si (A15), and Mo5SiB2 (T2) have been produced through the reaction of molybdenum, Si3N4, and BN powders. Formation of the intermetallics was examined by thermo-gravimetric and x-ray diffraction analysis. Densities of 94% of theoretical were achieved from pressureless sintering at 1,600°C. Microstructure examination using scanning electron microscopy and electron backscatter diffraction analysis shows that this powder metallurgy approach yields a fine dispersion of intermetallics in a molybdenum matrix with grain sizes on the order of 1–4 µm. The formation of Mo-Si-B alloys from the nitride-based reactions uses standard powder processing methods and provides a method for creating these materials in a much less complex and expensive manner than has been previously demonstrated.

HLADKY-HENNION, Anne-Christine/0000-0001-6339-8448 WOS: 000250278400011 PubMed: 18019236 Traditional flextensional transducers classified in seven groups based on their designs have been used extensively in 1-100 kHz range for mine hunting, fish finding, oil explorations, and biomedical applications. In this study, a new family of small, low cost underwater, and biomedical transducers has been developed. After the fabrication of transducers, finite-elements analysis (FEA) was used extensively in order to optimize these miniature versions of high-power, low-frequency flextensional transducer designs to achieve broad bandwidth for both transmitting and receiving, engineered vibration modes, and optimized acoustic directivity patterns. Transducer topologies with various shapes, cross sections, and symmetries can be fabricated through high-volume, low-cost ceramic and metal extrusion processes. Miniaturized transducers posses resonance frequencies in the range of above 1 MHz to below 10 kHz. Symmetry and design of the transducer, polling patterns, driving and receiving electrode geometries, and driving conditions have a strong effect on the vibration modes, resonance frequencies, and radiation patterns. This paper is devoted to small, multimode flextensional transducers with active shells, which combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. The performance of the transducers is emphasized.

Potential interconnect alloys of Fe–Cr and Fe–Ni–Cr were fabricated via extrusion of metal oxide pastes followed by heat treatment in hydrogen. Thermal expansion of the different alloys was measured and compared with that of yttria-stabilized zirconia (YSZ). Oxidation experiments were performed in air at 700 °C using cyclic heating and weighing, as well as thermogravimetric analysis. Additions of chromium to a Fe50Ni alloy were found to improve oxidation resistance although the performance of Fe–Ni–Cr compositions was inferior to Fe–Cr alloys of similar chromium content. The improvement in oxidation behavior with increasing chromium content of the Fe–Ni–Cr alloys was contrasted with the negative impact of the chromium addition on thermal expansion matching with YSZ. Binary Fe–Cr alloys such as Fe20Cr appear to be better suited for use as a SOFC interconnect compared with Fe42.5Ni15Cr and other similar Fe–Ni–Cr alloys.

A method for the rapid fabrication of homogeneous potential interconnect alloys from metal oxide precursors and evaluation of their thermal expansion mismatch to solid oxide fuel cells is described. Pastes of metal oxide powders were extruded into honeycomb geometries and sintered in hydrogen. Thermal expansion mismatch was evaluated based on heating with a zero-mismatch at room temperature, and on cooling with zero-mismatch temperatures at 600 or 1100∘C. The non-linear expansion behavior of Fe-Ni invar alloys resulted in different compositions being optimum, based on the assumed zero-mismatch temperature.

The goal of this study is to develop practices for evaluating and predicting the microstructural evolution of directly reduced iron-chromium alloys. This fundamental knowledge is being applied to a process developed at the Georgia Institute of Technology to fabricate metal honeycomb extrusions. A paste composed of oxide powders, binders and lubricants is extruded through a die of the desired cross-section and subsequently reduced to metal with hydrogen. The effects of time, temperature and composition on the extent of reduction and diffusion in reducing Fe2O3-Cr2O3 powder mixtures is investigated. The thermodynamics and kinetics of Fe2O3-Cr2O3 reduction are evaluated in terms of the free energy of formation as well as reducing species. The kinetics of the microstructural changes are evaluated through diffusion measurements. A thermodynamic model for Fe2O3-Cr2O3 was developed and used to determine the maximum amount of Cr2O3 that would reduce when in contact with iron as a function of the $\frac{P_{H_{2}}}{P_{H_{2}O}}$ ratio . Diffusion studies consisted of Fe-Cr2O3 couples held at temperature in a reducing atmosphere. Cr diffusion in Fe showed a concentration dependence for the geometries investigated.

Extrusion of oxide powders allows fabrication of thin-walled metal articles to produce controlled-geometry, low-density copper alloy architectures. Shapes formed with copper oxide powders mixed wit...

Cost has become a critical issue in the maturing technology of solid oxide fuel cells (SOFCs). While many seek new materials to improve cell performance, there comes a realization that the economics of fabricating a functional stack may drive commercialization faster than any performance issue. To this end, a novel fabrication technique is described which allows the simultaneous fabrication of both electrolytes and interconnects in a single hermetic package. Two key issues in this design involve the fabrication of honeycomb structures and the reduction of metal oxides during the sintering process to develop integral interconnects. The result is a highly scalable and cost effective method to produce SOFC stacks.

The major goals of this research project are to investigate the coupling of Linear Cellular Alloys (LCAs) as casings for reactive (thermite) fillers as high-energy-density structural energetic materials. The specific objectives include performing fundamental studies to: (a) investigate mechanics of dynamic densification and reaction initiation in Ta+Fe2O3 and Ta+Bi2O3 thermite powder mixtures and to (b) design and fabricate LCAs of intent (maraging steel) and reactive (tantalum) metals with cell geometries that provide stress transfer for chemical reaction initiation in the thermite filler and allow controlled fragmentation.

A new process has been developed to form hollow aluminum alloy spheres directly from the melt. These spheres are hermetic and have a relatively constant wall thickness and diameter. Spheres are formed through a pair of coaxial nozzles. The inner jet sustains a flow of inert gas while the annulus formed between the inner and outer jets carries a stream of molten metal. Axisymmetric instabilities in the hollow liquid metal jet result in pinched off bubbles that solidify as they fall through a flow controlled, inert atmosphere. Pure aluminum, eutectic aluminum-silicon, and aluminum-2% calcium were investigated as sphere producing materials. Al-2%Ca showed the most promise, due at least in part to the presence of oxide particles. Oxide particles promoted sphere stability and increased solidification rates.

Ceramic hollow spheres are being developed for electronic uses in piezoelectric transducers and low dielectric constant substrates, for structural applications in syntactic and metal foams, for fluid transport uses in filters and radiant burners, and for acoustic insulation. Fabrication of coarse hollow spheres (1–10 mm) is by nozzle or sacrificial core processes and fine sizes (1–100 microns) are fabricated using sol-gel techniques.

A line-of-sight vapour deposition process is used to form a low-voltage field emission cathode structure on the surface of an oxide-metal eutectic composite etched to expose arrays of single-crystal tungsten fibres. A SiO2 insulating film is first deposited, forming cone-shaped deposits on the tips of the exposed fibres. These cones act as a shadow mask for the subsequent deposition of a metal film. After removal of the cones, the metal film forms a grid-like structure with concentric apertures centered on each fibre tip. Application of a potential of less than 100 V between the metal grid and the base of the fibres produces an electric field at the fibre tips of sufficient intensity to produce field emission. The equilibrium geometry of the deposits which form on the fibre tips (cathode cones) is such that there is a linear relationship between the height of the cone and its diameter. There is also a direct correlation between the cathode cone angle, which depends on the material being deposited, and the cone angle of the insulator film. For SiO2, the cathode cone angle was determined to be 37°, while the cone angle of the insulator film was 26°. Comparison of the theoretical values of the lateral growth velocity of the cathode cones with values determined from experimental measurements indicated that the maximum sticking coefficient was independent of the growth angle, η, for SiO2, but varied as a function of cos η for molybdenum. A multiple deposition process was developed which permitted independent control of the interelectrode spacing and insulator film thickness.

The dynamic deformation and fragmentation response of 25% dense 9-cell linear cellular alloy (LCA) made of unaged 250 maraging steel, fabricated using a direct reduction and extrusion technique, is investigated. Explicit finite element simulations were implemented using AUTODYN finite element code. The maraging steel properties were defined using a Johnson-Cook strength model with previously validated parameters. Rod-on-anvil impact tests were performed using the 7.6mm helium gas gun and the transient deformation and fragmentation response was recorded with highspeed imaging. Analysis of observed deformation states of specimens and finite element simulations reveal that in the case of the 9-cell LCA, dissipation of stress and strain occurs along the interior cell wells resulting in significant and ubiquitous buckling prior to confined fragmentation.

New structural alloys based on borosilicides of molybdenum have been considered as potential replacements for current Ni-base superalloys, as they show promise as highly oxidation- and creep-resistant materials while still maintaining a moderate level of damage tolerance. Two alloys, each composed of Mo-3Si-1B (wt.%) with nominally similar fine-grained microstructures, have been developed utilizing markedly differing processing routes. Here, we study the influence of processing route on the fracture toughness of alloys containing ∼55 vol.% ductile α-Mo and ∼45 vol.% brittle intermetallics (Mo 3 Si (A15) and Mo 5 SiB 2 (T2)). The room temperature toughness of these two alloys is significantly lower than that of previously evaluated coarser-grained Mo-Si-B alloys with similar composition; however at 1300 °C, the crack-initiation toughness of the fine- and coarse-grained alloys are nearly identical. At lower temperatures, the current finer-grained materials behave in a brittle manner as the smaller grains do not provide much impediment to crack extension; cracks can advance with minimal deflection thereby limiting any extrinsic toughening. Plastic constraint of ductile α-Mo grains by the hard intermetallic grains also serves to lower the toughness. Silicon impurity concentrations in the grain boundaries in the fine-grained alloys are much higher, leading to lower grain-boundary strengths and contributing to the much lower room temperature initiation toughnesses of these alloys (no stable crack growth was observed), as compared to the coarser-grained alloys. At 1300 °C, the increased ductility of α-Mo allows for significant plasticity; the correspondingly much larger contribution from intrinsic toughening results in significantly enhanced toughness, such that the finer grain morphology becomes less important in limiting crack growth resistance. Further optimization of these alloys, however, is still required to tailor their microstructures for the mutually exclusive requirements of oxidation resistance, creep resistance and damage tolerance.

Millimeter-sized, hollow spheres of lead zirconate titanate were fabricated by blowing gas through a fine-grained slurry of PZT-5. After they were sintered, the spheres were poled in two ways: radially between inside and outside electrodes, and tangentially between two outside electrodes. The capacitance and vibration modes were modeled and measured for these two poling configurations. The two principal modes of vibration were a breathing mode near 700 kHz and a wall thickness mode near 10 MHz. These spheres have potential uses in medical ultrasound, nondestructive testing, and low-density transducer arrays.

WOS: 000230440100003, Ultrasonic probes that can withstand high pressures and temperatures are needed for deep oil wells, underwater sonar systems, the processing of chemicals, and as automotive actuators. Pressure limits of hollow spherical lead zirconate titanate hydrophones with diameters in the range of 0.5-3.0 mm and wall thicknesses of 50-300 mu m have been evaluated using both experimental data and finite element analysis. The spheres were tested at hydrostatic pressures up to 70 MPa (10, 000 psi, 7000 meters) and temperatures of 25 degrees C-200 degrees C The results of the tests and analyses indicate that, at room temperature, unelectroded spheres of all sizes within this size range can withstand pressures up to 7 MPa (1000 psi) and that smaller spheres can survive up to 70 MPa (10, 000 psi). Combined temperature-pressure tests on 2 mm spheres indicate survival at temperatures and pressures as high as 200 degrees C and 28 MPa (4, 000 psi). Preliminary poling studies indicate that depoling may become a problem at high pressures and elevated temperatures.

The program objective is to develop SOFCs, operating in the 500-700 degrees C range, based on Metal/Electrolyte square cell honeycomb formed by simultaneous powder extrusion of electrolyte and metal interconnects on alternate layers. The alloy interconnect is being formed as an oxide powder mixture which will be reduced to the metal and then co-sintered with the electrolyte during hydrogen thermal treatment. Goals include power density of 5 KW/liter, alternative fuels, designed thermal management, and low fabrication cost. The project is divided into electrolyte/electrode development, fabrication of hybrid and electrolyte monoliths, and thermo-mechanical stress modeling and heat transfer. Honeycomb fuel cells offer a great potential for high-power density and low-cost manufacturing. Also, producing multiple layers simultaneously forms a gas-tight high temperature seal in a single step, minimizing or eliminating difficulties encountered in other designs (planar or tubular) of SOFCs. The unique honeycomb cell geometry, however, poses some challenges in application of electrodes with desired microstructures to the honeycomb channels. However, near the end of the program, success was obtained in reduction and co-sintering of crack free, hermetic SOFC platform with alternating layers of metal interconnect and YSZ electrolyte. The structures were electroded and operated as fuel cells at modest powder levels. In, monolithic, all YSZ, honeycomb fuel cells, power levels of 0.09 W/sq cm of electrolyte area, 0.30 W/cu cm of call volume, and 0.15 W/g was achieved in the program.

This project was a feasibility study to explore the viability of using metal honeycomb technology developed at Georgia Tech as an economical alternative to processing titanium structures of relevance to aerospace applications. In the first part of this program, honeycombs with square prismatic cells were fabricated by extrusion of titanium oxide powder and experiments were conducted to convert the sintered honeycomb to metallic titanium through electrolytic reduction. This approach was pursued to explore extension of the FFC process 1 to electrolysis of this wall ( 300 m) Ti02 structures as the reduction stage of our proposed process. These tests focused on kinetics of titanium reduction because high specific surface area oxide performs can be fabricated using technology developed by the lightweight structures group at Georgia Tech2-4 via extrusion of thin walled, small cell size, honeycomb structures from powders/binder mixtures. During the honeycomb reduction studies, dendritic electrodeposition of titanium was observed to be occurring similar to the Hall process for aluminum. Thus, a series of tests were conducted to determine if high purity titanium could be electrodeposited from a molten salt saturated with titanium ore. Our conclusion was that this process is occurring and because this approach has potential for being of significant economic value, a provisional patent application has been filed.

A novel method of fabricating low-density hollow sphere metallic foam has been developed. Utilizing pre-existing technology, thin-wall, hollow oxide spheres, ∼ 2mm in diameter, were formed from powder slurries with a coaxial nozzle process. Oxide foams were constructed by bonding sintered spheres at points of contact and firing. The oxide foams were reduced to the metallic state in a hydrogen atmosphere. Successful precursor compositions for transformation included NiO, Cu2O, and NiO-Cu2O. After reduction, the metal foams were sintered to increase strength and resulting foam densities were generally 10–20% of theoretical density. Wall thickness of the spheres which constitute the foams ranged from 50–100 μ m. Nickel foams were crushed under uniaxial compressive stress, and mechanical properties (yield stress, elastic modulus, and energy absorption) were investigated under varying density in order to determine parametric relationships to compare to existing models of foam properties. The effects of sintering, reduction, and compressive deformation on the microstructures were examined with SEM and EDS.

Mechanical behavior of hollow ceramic spheres was evaluated using finite element analysis. Failure mode and strength of spheres were determined from stress analysis. A parametric study of strength as a function of wall thickness to sphere diameter ratios indicated that strength is a function of relative density squared. Strength of aluminium oxide hollow spheres made by the coaxial nozzle powder process agreed well with the finite element parametric model.

Bonded hollow sphere foams for this study were made from point-contact, slurry-bonded monosized spheres, 2.5 mm in diameter. The permeabilities of these foams are compatible with the diffuser base in radiant burners. For this study, the effect of quantity of bonding phase on interstitial porosity, permeability, and uniformity of gas flow through the foams was investigated. The relationship between permeability and porosity was modeled with the Kozeny-Carman equation. Attempts were made to correlate diffuser base permeability to operating characteristics of these burners.

This paper describes the design and performance of a small, high-frequency, piezoelectric, underwater probe. The probes are fabricated from miniature, thin-wall, lead zirconate titanate ceramic hollow spheres with radii (r) from 0.5 mm to 2.5 mm and wall thickness (t) from 50 ?m to 250 ?m. The experimental results reported in this paper are focused on devices prepared from hollow spheres with an outer radius of 1.38 mm and a mean wall thickness of 75 ?m. As a hydrophone, these devices display a sensitivity of ?220.7 dB re 1 V ?Pa?1 at 250 kHz that stays flat to within ?3 dB over the frequency range from 10 kHz to 450 kHz with an omnidirectional response. Within the accessible range of sphere sizes (r = 0.5?2.5 mm, t = 50?250 ?m), this stable and flat sensitivity behavior could be extended to a range from ?212 to ?225 dB re 1 V ?Pa?1 and up to 1 MHz. Finite element analysis of this transducer using the ATILA? software is also included in this paper, comparing the computational results with the results from the experimental measurements. Based on the excellent agreement obtained, a parametric modeling study was also undertaken and its results are discussed in this paper. The miniature ceramic hollow-sphere transducers fill a gap in the frequency range of 200 kHz to 1 MHz with an omnidirectional response and much higher sensitivity than other ceramic and polymer piezoelectric probes.

Ion implantation of silicon ions into sapphire and polycrystalline alumina followed by heat treatment resulted in the precipitation of mullite. A dose of 1 × 1018 Si+ /cm2 followed by a heat treatment at 1400‡ C produced an interlocking mullite surface layer with a needle morphology which was identifiable by x-ray diffraction (XRD). The lower thermal expansion coefficient of mullite compared to alumina produces a compressive surface layer on cooling from the annealing temperature and is evidenced by observations of Vickers indentations. Annealing at 1400‡ C resulted in a 30% increase in fracture toughness for sapphire and more importantly, an increase of 30% was also observed for polycrystalline alumina substrates. The effect of silicon implantation on the microhardness of sapphire and on the modulus of rupture of implanted polycrystalline alumina was also measured and is reported.

In order to determine in what ways ion implantation and subsequent heat treatment can be used to improve mechanical properties of ceramics, (110) yttria stabilized zirconia (YSZ) was implanted with Al+ or Zr+ ions and heat treated at a series of temperatures. Ion doses from 1016 to 4 × 1017 ion cm 2 were used, with annealing temperatures up to 1575°C. In Al+ implanted samples, many small precipitates formed at temperatures of about 1200δC, while at higher temperatures, the alumminum was precipitated as micro-sized alumina crystallites with 10–20% increases in hardness and fracture toughness. However, by allowing sufficient time for the nucleation of a large number of precipitates in the 1150 to 1250°C range, a new nucleation controlled microstructure (NCM) was formed, consisting of interlocking zirconia and alumina phases which exhibited improvements of 50% in fracture toughness and 25% in hardness.

In an effort to transformation toughen alumina surfaces, Y+ was implanted in sapphire previously implanted with Zr+ at a dose of 1.25 x 1017 ions/cm2. The Y+ implant doses ranged from 1 to 10 x 1015 ions/cm2 and the double implants were labelled Y+/Zr+/A12O3. Annealing in the air at 1400‡ C produced a uniform surface film of polycrystalline ZrO2 doped with Y2O3 which had a grain size of 0.1 to 1.0 Μm. From x-ray diffraction (XRD), the ZrO2 phases transitioned from monoclinic to tetragonal to cubic as the Y2O3 content increased from 0 to 4 m/o based on zirconia content. Obtaining only cubic zirconia was surprising, because pure cubic ZrO2 should result only above 9.2 m/o Y2O3. The ratios of Y to Zr measured by electron spectroscopy for chemical analysis (ESCA) depth profiling for the high dose Y+ implant was equivalent to 10 m/o Y2O3 in ZrO2 rather than the implanted ratio of 4 m/o. The higher than expected Y concentrations agreed with the XRD results and were probably produced by Zr removal by ion milling during the high Zr+ dose implant. Surface fracture toughness, as measured by indentation, decreased as yttria content increased because elimination of monoclinic ZrO2 from the precipitate phases prevented a surface compression layer created by the tetragonal to monoclinic ZrO2 transition on cooling from annealing temperatures.

Microstructure of precipitates produced by annealing ion implanted surfaces have been investigated in the Al2O3-ZrO2 system and both microhardness and indentation fracture toughness have been measured for correlation with microstructure. Air annealing of 190 keV high dose implants of Al+ in yttriastabilized zirconia and Zr+ in AI2O3 have resulted in A12O3 and ZrO2 precipitates, respectively, as would be expected from phase equilibria. However, annealing schedules drastically alter precipitate microstructure (i.e., crystallite size, morphology, orientation), and changes in microstructure have produced significant variation of surface mechanical properties. Crystallization of the ZrO2 films on AI2O3 was observable by conventional XRD. The precipitated ZrO2 was in the monoclinic structure if the grain size was large or in the tetragonal state if grain size was small. Being able to produce tetragonal ZrO2 particles in A12O3 surfaces suggests the possibility of transformation toughening and strengthening.

Single crystal yttria stabilized zirconia was implanted with 100 keV Ca+, Al+, and O2+ ions at fluences of 1015 to 6 × 1016 ions/cm2; . Blistering was observed at doses of 3 × 1016; O2;+ cm−2; and 6 × 1016; Al+ cm−2; but none was evident with Ca+. Knoop microhardness with a shallow indenter penetration depth peaked at a dose of 1016; ions/cm−2; for both Al+ and O2;+ but Ca+ produced no effect on microhardness. Vicker's microhardness with a much greater indenter penetration depth was not changed detectably by implantation but fracture toughness measurements from the same Vicker's indentations exhibited 10–23% increases at the highest O2+ doses and 20–25% increases at high Al+ doses. Annealing the highest implant doses at 1200° reduced the fracture toughness to pre-implant levels. Reflection electron diffraction showed that the surface had not been made amorphous by the 6 × 1016; Al+ dose as a well crystallized diffraction pattern was obtained.