In this dissertation, nano-manufacturing of amorphous alloys for electro-catalytic applications is reported and the role of chemistry and active surface area on catalytic behavior is discussed. The catalytic activity of recently developed platinum and palladium-based metallic glasses was studied using cyclic voltammetry and localized electrochemical techniques. The synergistic effect between platinum and palladium was shown for amorphous alloys containing both these elements. The mechanism for superior catalytic behavior was investigated through electronic structure and surface chemical state of the alloys. A correlation between the work function and catalytic performance of the amorphous alloys with widely varying chemistries was established. To address the high cost associated with the noble-metal containing catalysts, the performance of non-noble Ni-P amorphous catalyst was evaluated for electro-catalysis. A facile pulsed electrodeposition approach was used for the nano-manufacturing of these amorphous catalysts. This nano-manufacturing route allowed the synthesis of fully amorphous nano-wires at room temperature for alloys with little or no noble-metal content. A wide range of nano-wires with varying aspect ratios from 25 to 120 was synthesized using commercially obtained anodic aluminum oxide (AAO) nano-molds. Cyclic voltammetry and chrono-amperometry demonstrated superior performance in terms of electrocatalytic activity and stability of the metallic glass nano-wires towards electro-oxidation …

Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their effects on fracture toughness, hardness and flexural strength are shown. Mechanical testing of Vickers hardness, 3-point bend and Chevron notch was done and the microstructural effects on the resulting mechanical properties are investigated.

High entropy alloys (HEAs) are a new class of solid solution alloys that contain multiple principal elements and possess excellent mechanical properties, from corrosion resistance to fatigue and wear resistance. Even more recently, twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) non-equiatomic high entropy alloys have been engineered, promising increased strength and ductility as compared to their equiatomic counterparts. However, impact and fracture resistance of these HEAs has not been studied as much as their other mechanical properties. In this thesis, the hardness, tensile properties, and Charpy impact energy of Al0.3CoCrFeNi, a TWIP HEA, and 50Fe-30Mn-10Co-10Cr (at.%), a TRIP HEA, was explored. First, three processing conditions, (1) as-received, (2) recrystallized, and (3) peak hardness, were chosen for each alloy and verified with Vickers microhardness measurements. Next, the tensile properties of each alloy and condition were investigated. Charpy impact specimen size was then selected based on the final plate thickness, and the machined samples were tested. Plastic zone size and change in sample thickness in the deformed region of each condition after testing was measured. Post-impact test inspection of the samples in all conditions showed that the samples were in tension near the V-notch root and in compression at the …

This dissertation tested the hypothesis that pulsed laser deposition (PLD) could be used to create targeted dopant profiles in few layered WS2 films based on congruent evaporation of the target. At the growth temperatures used, 3D Volmer-Weber growth was observed. Increased energy transfer from the PLD plume to the growing films degraded stoichiometry (desorption of sulfur) and mobility. Sulfur vacancies act as donors and produce intrinsic n-type conductivity. Post deposition annealing significantly improved the crystallinity, which was accompanied by a mobility increase from 6.5 to 19.5 cm2/Vs. Preparation conditions that resulted in excess sulfur, possibly in the form of interstitials, resulted in p-type conductivity. Current-voltage studies indicated that Ohmic contacts were governed by surface properties and tunneling. Extrinsic p-type doping of few layered WS2 films with Nb via pulsed laser deposition using ablation targets fabricated from WS2, S and Nb powders is demonstrated. The undoped controls were n-type, and exhibited a Hall mobility of 0.4 cm2/Vs. Films doped at 0.5 and 1.1 atomic percentages niobium were p-type, and characterized by Fermi levels at 0.31 eV and 0.18 eV from the valence band edge. That is, the Fermi level moved closer to the valence band edge with increased doping. With increased …

The current understanding of the mechanical properties and deformation behavior of some individual phases in titanium alloys is limited due to the fine scale at which these phases precipitate within the β-phase matrix. The α and ω phases represent the most widely observed phases in titanium alloys depending on the alloy composition and also the heat treatment procedure adopted during processing. The possibility of precipitating ω-phase depends on the content of the β-stabilizers within the system. Although a significant compositional partitioning occurs within ω-phase upon aging treatment, the knowledge of ω-phase mechanical properties as a function of composition is very limited. The initial part of the current work focuses on the effect of common β-stabilizers elements on the phase stability and mechanical properties of the ω-phase using first-principles calculations. A relation between the bonding nature, the phase stability, and elastic properties was proposed. Thereafter αʺ martensitic phase was investigated in Ti-Nb and Ti-Nb-O alloys. The phase stability and martensitic start temperature of αʺ-phase was studied as a function of Nb and oxygen content. Also, the effect of the lattice shear distortion induced by oxygen atom on stabilizing β-phase was investigated. Subsequently the effect of the β-stabilizers' elements on stacking faults …

In the current study, we have investigated the cyclic loading behavior of conventional as well as novel alloy system exhibiting fine and ultrafine-grained structure. While in case of conventional alloy systems (here aluminum alloy AA5024), the effect of three different grain sizes was investigated. Improvement in fatigue properties was observed with decreasing grain size. The unique microstructure produced via Friction stir processing was responsible for the improved fatigue response. Additionally, microstructures consisting of a high fraction of special boundaries within the fine and ultrafine-grained regime were also subjected to cyclic loading. The hierarchical features introduced in the eutectic high entropy alloy deflected the persistent slip bands, responsible for fatigue cracking, thus resulted in delayed crack initiation and improved fatigue life. The selective nature of fatigue was learnt in the fine grain Al0.5CoCrFeNi, where the introduction of hierarchical features did not result in improved fatigue properties. The weak links in the microstructure, while not affecting the tensile properties, got exposed during cyclic loading. Further study on the medium entropy alloy revealed the inherent reason for the improved fatigue properties. The medium entropy alloys utilized the benefit of UFG single-phase FCC matrix. The UFG matrix showed signs of transformation of FCC phase …

High entropy alloys (HEAs) based on refractory elements have shown a great potential for high temperature structural applications. In particular, the ones containing Al, exhibits a microstructure similar to the γ-γ' in Ni-based superalloys. While these alloys exhibit impressive strengths at room temperature (RT) and at elevated temperatures, the continuous B2 matrix in these alloys is likely to be responsible for their brittle behavior at RT. Phase stability of five such alloys are studied by thermo-mechanical treatments and characterization techniques using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Two of these alloys showed an inverted microstructure, where the disordered BCC phase becomes continuous, and therefore, they were characterized in detail using SEM, TEM, atom probe tomography (APT) and synchrotron x-ray diffraction experiments. The phenomenon of phase inversion lead to a better combination of strength and ductility as compared to the non-inverted microstructure.To enhance the stability of B2 intermetallic phase which provides the strength when present in a BCC matrix, multicomponent B2 phase compositions stable at 1000°C in some of the above studied alloys, were melted separately. The aim was to establish a single phase B2 at 1000°C and understand the mechanical behavior of these single-phase multicomponent B2 intermetallic …

High entropy alloys (HEAs) are a relatively new class of solid solution alloys that contain multiple principal elements to take advantage of their high configurational entropy, sluggish diffusion, lattice distortion, and the cocktail effect. In recent development, work hardening mechanisms known as twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) have been found active in Al0.3CoCrFeNi (molar fraction) and Fe50Mn30Co10Cr10 (at %) HEA compositions. Friction-stir processing was done to increase the mechanical properties and improve the microstructure of the alloys for the purpose of high strain rate performance. Quasi-static tensile tests as well as top-hat geometry Split-Hopkinson pressure bar tests were conducted to view the mechanical properties as well as view the microstructural evolution at dynamic strain rates. Overall, the Al0.3CoCrFeNi condition after friction-stir processing and heat treatment has proved to have the best mechanical properties, and selecting from the conditions in this study, Al0.3CoCrFeNi has better shear localization resistance.

Lithium-sulfur (Li-S) batteries are faced with practical drawbacks of poor cycle life and low charge efficiency which hinder their advancements. Those drawbacks are primarily caused by the intrinsic issues of the cathodes (sulfur) and the anodes (Li metal). In attempt to resolve the issues found on the cathodes, this work discusses the method to prepare a binder-free three-dimensional carbon nanotubes-sulfur (3D CNTs-S) composite cathode by a facile and a scalable approach. Here, the 3D structure of CNTs serves as a conducting network to accommodate high loading amounts of active sulfur material. The efficient electron pathway and the short Li ions (Li+) diffusion length provided by the 3D CNTs offset the insulating properties of sulfur. As a result, high areal and specific capacities of 8.8 mAh cm−2 and 1068 mAh g−1, respectively, with the sulfur loading of 8.33 mg cm−2 are demonstrated; furthermore, the cells operated at a current density of 1.4 mA cm−2 (0.1 C) for up to 150 cycles. To address the issues existing on the anode part of Li-S batteries, this work also covers the novel approach to protect a Li metal anode with a thin layer of two-dimensional molybdenum disulfide (MoS2). With the protective layer of MoS2 …

Thermoelectric (TE) devices can undergo degradation from reactions in corrosive environments and at higher operating temperatures by sublimation and oxidation. To prevent the degradation, we have applied two high temperature polymers (HTPs) as coatings for TE materials. Sintering temperatures were from 250°C to 400°C. We explain why dip coating is better technique in our study and had two potential HTPs for tests. By applying TGA (thermogravimetric analysis), we were able to figure out which HTPs have better thermal resistivity. Besides, TGA also help us to find proper curing cycles for HTPs. EDS and SEM results show that the coatings prevent oxidation and sublimation of TE materials. We also shorten HTP curing cycle time and lower the energy costs.

Geckos are famous for the skill of switchable adhesion that they use to stick on various surface while keep their fingers super clean. In the dissertation, a unique mechanism was discovered to explain gecko self-cleaning phenomena. Using atomic force microscopy (AFM), we managed to compare the microparticle-substrate adhesion and the microparticle-seta adhesion with a single seta bonded to the AFM cantilever. A dynamic effect was approved that high pulling-off speed could increase the microparticle-substrate adhesion and thus the self-cleaning appears at high moving speed. Based on the self-cleaning theory, a gecko-inspired N-doped graphene surface with switchable adhesion was achieved, which was designed into a bio-inspired micromanipulator with a success rate over 90%. When electrical bias was applied on this biomimetic surface, the charge concentration induced an electrical double layer (ELD) on the convex surfaces, which attracts polar water molecules to form a water bridge on it, significantly enhancing the adhesion on the wrinkled graphene surface, mimicking the capillary force on beetle feet. Therefore, the bio-inspired adhesive surface can be controlled with speed, electrical bias, humidity and different material surfaces. The water attraction phenomenon on the polarized surface was further tested for the potential application of water collection and evaporation in …

Through a series of carefully designed experiments, characterization and some modeling tools, this work is aimed at studying the role of thermal profiles on different microstructural zones and associated properties like strength and corrosion through a variation of weld parameters, thermal boundary conditions and material temper. Two different alloys belonging to the Al-Cu and Al-Cu-Li system in different temper conditions- peak aged (T8) and annealed (O) were used. A 3D-thermal pseudo mechanical (TPM) model is developed for the FSW process using heat transfer module in COMSOL Multiphysics and is based on a heat source wherein the temperature dependent yield shear stress is used for the heat generation. The precipitation and coarsening model is based on the Kampmann and Wagner theoretical framework and accounts for the competition between the various nucleation sites for both metastable and equilibrium precipitates. The model predicts different precipitate mean radius and volume fraction for the various zones in the friction stir welded material. A model for the yield strength is developed which considers contributions from different strengthening mechanisms. The predictions of the each models have been verified against experimental data and literature. At constant advance per rotation, the peak temperature decreases with a decrease in traverse …

This thesis describes the fabrication and characterization of two-dimensional transition dichalcogenides (2D TMDs) nanolayers for various applications in electronic and opto-electronic devices applications. In Chapter 1, crystal and optical structure of TMDs materials are introduced. Many TMDs materials reveal three structure polytypes (1T, 2H, and 3R). The important electronic properties are determined by the crystal structure of TMDs; thus, the information of crystal structure is explained. In addition, the detailed information of photon vibration and optical band gap structure from single-layer to bulk TMDs materials are introduced in this chapter. In Chapter 2, detailed information of physical properties and synthesis techniques for molybdenum disulfide (MoS2), tungsten disulfide (WS2), and molybdenum ditelluride (MoTe2) nanolayers are explained. The three representative crystal structures are trigonal prismatic (hexagonal, H), octahedral (tetragonal, T), and distorted structure (Tʹ). At room temperature, the stable structure of MoS2 and WS2 is semiconducting 2H phase, and MoTe2 can reveal both 2H (semiconducting phase) and 1Tʹ (semi-metallic phase) phases determined by the existence of strains. In addition, the pros and cons of the synthesis techniques for nanolayers are discussed. In Chapter 3, the topic of synthesized large-scale MoS2, WS2, and MoTe2 films is considered. For MoS2 and WS2 films, the …

Recent progress in layered transition metal dichalcogenides (TMDs) has led to various promising electronic and optoelectronic applications. However, the structure of materials plays a critical role in electronic and optoelectronic devices, and determines performance. Electronic and optoelectronic devices typically consist of multiple layers that form electrical homojunctions or heterojunctions. Therefore, in a device it can be expected that a WS2 layer may serve as the substrate for a subsequent layer in a multilayer device stack and determine how the layer grows. In transistor structures, roughness at the channel/gate dielectric interface introduces field variations and charge scattering. Therefore, understanding the relations between processing, surface morphology and properties is important. In this project, the effects of pulsed laser deposition (PLD) processing conditions on the surface morphology of few layered WS2 films were studied. WS2 films were synthesized under processing conditions that represent the extremes of surface supersaturation and kinetic energy transfer from the flux to the growing films, and evolution of the surface morphology was studied. The specific conditions were 1Hz/50mJ, 10Hz/50mJ, 1Hz/300mJ, and 10Hz/300mJ respectively. Combining AFM, XRD and Raman analyses, it was determined that deposition at 10Hz/300mJ, provided the best structural properties and surface morphology. Growth appeared to be 3D-cluster, …

In this dissertation, density functional theory calculations are performed to calculate the thermodynamic and electrochemical properties of metal coordinated frameworks for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Gibb's free energy, overpotential, charge transfer and ligands effect are evaluated. The charge transfer analysis shows the positive charges on the metal coordinated frameworks play an essential role in improving the electrochemical properties of the metal coordinated frameworks. Based on the calculations, design principles are introduced to rationally design and predict the electrochemical properties of metal coordinated frameworks as efficient catalysts for ORR and OER. An intrinsic descriptor is discovered for the first time, which can be used as a materials parameter for rational design of the metal coordinated frameworks for energy storage and conversion. The success of the design principles provides a better understanding of the mechanism behind ORR and OER and a screening approach for the best catalyst for energy storage and conversion.

An environmentally friendly, and contamination free process for etching and cleaning semiconductors is critical to future of the IC industry. Under the right conditions, water has the ability to meet these requirements. Water becomes more reactive as a function of temperature in part because the number of hydronium and hydroxyl ions increase. As water approaches its boiling point, the concentration of these species increases over seven times their concentrations at room temperature. At 150 °C, when the liquid state is maintained, these concentrations increase 15 times over room temperature. Due to its enhanced reactivity, high temperature water (HTW) has been studied as an etch and clean of thermally grown SiO2, Si3N4, and low-k films. High temperature deuterium oxide (HT-D2O) behaves similarly to HTW; however, it dissociates an order of magnitude less than HTW resulting in an equivalent reduction in reactive species. This allowed for the effects of reactive specie concentration on etch rate to be studied, providing valuable insight into how HTW compares to other high temperature wet etching processes such as hot phosphoric acid (HPA). Characterization was conducted using Fourier transform infrared spectroscopy (FTIR) to determine chemical changes due to etching, spectroscopic ellipsometry to determine film thickness, profilometry to …

Silicon nitride on steel sliding contacts may provide advantageous tribological properties over traditional self-mated pairs, however the friction and wear behavior at high sliding speeds (>1 m/s) is not well understood. Previous studies at low sliding speeds (< 1 m/s) have found that the wear mechanisms change as a function of the operating parameters, e.g. atmosphere, sliding speed, load, and temperature, due to the formation of transition metal oxides such as Fe2O3 and Fe3O4. This study detected transient effects of the dry silicon nitride on steel contact over a range of sliding speeds to understand their relation to tribochemical reactions and the resulting tribological behavior. Two sets of dry silicon nitride on steel experiments were conducted at 1.45 GPa maximum Hertzian pressure. The first set were low sliding speed reciprocating experiments, conducted at an average of 0.06 m/s, conducted at variable operating temperature, ranging from 23 °C to 1000 °C. In the low sliding speed experiments, transitions of the wear mechanism from adhesive wear, to abrasive wear, then to oxidative wear was observed when the operating temperature increased. The second set were high sliding speed experiments, conducted at variable sliding speeds, ranging from 1 m/s to 16 m/s. In the …

Silicate glasses are the most common glass types and have impact on almost every aspect in our lives: from window, containers, to glass fibers for telecommunications. Unlike their crystalline counterparts, glass materials lack long-range order in their atomic arrangement but their structures do possess short and medium range characteristics that play critical roles in their physical and chemical properties. Despite active development of characterization techniques that have contributed to the understanding of glass structures, there remain key challenges in obtaining essential structural features of glasses. Atomistic computer simulations have become an increasingly important method in elucidating the atomic structures and in interpretation and/or prediction of composition-structure-property relationships of complex materials. In this dissertation, classical molecular dynamic (MD) simulations were used to investigate the atomic structures, dynamic and other properties of two important glass systems—aluminosilicate glasses and borosilicate glasses, which are the basis of most industrial and technologically important glasses. Firstly, a comprehensive study of peralkaline Na2O-Al2O3-SiO2 glass with varying Al2O3/SiO2, Na2O/Al2O3, Na2O/SiO2 ratios has been performed to obtain better understanding of the composition–structure–property relationships in this glass system. More than 99% of Al were 4-coordinated in these glasses, validating that Na+ tend to charge balance [AlO4]- network forming units first …

Dissimilar metals joining have been used in many industry fields for various applications due to their technique and beneficial advantages, such as aluminum-steel and magnesium-steel joints for reducing automobile weight, aluminum-copper joint for reducing material cost in electrical components, steel-copper joints for usage in nuclear power plant, etc. The challenges in achieving dissimilar joints are as below. (1) Big difference in physical properties such as melting point and coefficient of thermal expansion led to residual stress and defects. (2) The miscibility issues resulted in either brittle intermetallic compound layer at the welded interface for miscible combinations (such as, aluminum-steel, aluminum-copper, aluminum-titanium, etc.) or no metallurgical bonding for immiscible combinations (such as magnesium-copper, steel-copper, etc.). For metallurgical miscible combinations, brittle intermetallic compounds formed at the welded interface created the crack initiation and propagation path during deformational tests. (3) Stress concentration appeared at the welded interface region during tensile testing due to mismatch in elastic properties of dissimilar materials. In this study, different combinations of dissimilar metals were joined with friction stir welding. Lap welding of 6022-T4 aluminum alloy/galvanized mild steel sheets and 6022-T4 aluminum alloy/DP600 steel sheets were achieved via friction stir scribe technology. The interlocking feature determining the fracture mode …

First, the effect of transition metal oxide (e.g., V2O5, Co2O3, etc.) on the physical properties (e.g., density, glass transition temperature (Tg), optical properties and mechanical properties) and chemical durability of a simplified borosilicate nuclear waste glass was investigated. Adding V2O5 in borosilicate nuclear waste glasses decreases the Tg, while increasing the fracture toughness and chemical durability, which benefit the future formulation of nuclear waste glasses. Second, structural study of ZrO2/SiO2 substitution in silicate/borosilicate glasses was systematically conducted by molecular dynamics (MD) simulation and the quantitative structure-property relationships (QSPR) analysis to correlate structural features with measured properties. Third, for bioactive glass formulation, mixed-network former effect of B2O3 and SiO2 on the structure, as well as the physical properties and bioactivity were studied by both experiments and MD simulation. B2O3/SiO2 substitution of 45S5 and 55S5 bioactive glasses increases the glass network connectivity, correlating well with the reduction of bioactivity tested in vitro. Lastly, the effect of optical dopants on the optimum analytical performance on atom probe tomography (APT) analysis of borosilicate glasses was explored. It was found that optical doping could be an effective way to improve data quality for APT analysis with a green laser assisted system, while laser spot size …

The objective of this study was to increase the bond strength at the surface interface of a thin stainless-steel panel for structural bonding on a helicopter. To achieve this objective, six activation methods for applying the coating to the panel in the surface preparation process are presented and explored. Adhesion and roughness tests were conducted to determine which method consistently initiates the etch and improves the bond at the surface. Based on the test results, three methods proved to be effective in initiating the etch. Of the three effective methods, only one method exhibited significantly improved bond strength at the surface interface as well as consistently initiated the etch in solution. The applicability of this method is discussed, and recommendations are presented for further study.

Magnesium and its alloys are considered as the potential biomaterials due to their biocompatibility and biodegradable characteristics but suffer from poor corrosion performance. Various surface modification techniques are employed to improve their corrosion resistance. In present case, laser surface melting was carried out on AZ31B Mg alloy with various laser energy densities using a continuous wave ytterbium laser. Effect of laser treatment on phase and microstructure evolution was evaluated by X ray diffraction and scanning electron microscopy. Multi-physics thermal model predicted time temperature evolution along the depth of the laser treatment zone. Additionally, electrochemical method and bio-immersion test were employed to evaluate the corrosion behavior in simulated body fluid medium. Microstructure revealed grain refinement and even distribution of Mg17Al12 phase along the grain boundary for laser treated samples leading to substantial enhancement in the corrosion resistance of the laser treated samples compared to the untreated alloy. The laser processed samples also possessed a superior wettability in SBF solution than the untreated sample. This was further reflected in enhanced bio-integration behavior of laser processed samples. By changing the parameters of laser processing such as power, scanning speed, and fill spacing, a controllable corrosion resistance and bioactivity/biocompatibility of the implant material was …

The tribological properties of cold sprayed Ni-WC metal matrix composite (MMC) coatings were investigated under dry sliding conditions from room temperature (RT) up to 400°C, and during thermal cycling to explore their temperature adaptive friction and wear behavior. Characterization of worn surfaces was conducted using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy to determine the chemical and microstructural evolution during friction testing. Data provided insights into tribo-oxide formation mechanisms controlling friction and wear. It was determined that the steady-state coefficient of friction (CoF) decreased from 0.41 at RT to 0.32 at 400˚C, while the wear rate increased from 0.5×10-4 mm3/N·m at RT to 3.7×10-4 mm3/N·m at 400˚C. The friction reduction is attributed primarily to the tribochemical formation of lubricious NiO on both the wear track and transfer film adhered to the counterface. The increase in wear is attributed to a combination of thermal softening of the coating and a change in the wear mechanism from adhesive to more abrasive. In addition, the coating exhibited low friction behavior during thermal cycling by restoring the lubricious NiO phase inside the wear track at high temperature intervals. Therefore, cold sprayed Ni-WC coatings are potential candidates for elevated temperature and …

Acoustics is the study of all sound waves, with ultrasound classified as those frequencies above 20,000 Hz. Currently, ultrasound is being used in many industries for a variety of purposes such as ultrasonic imaging, ultrasonic assisted friction stir welding, and ultrasonic spot welding. Despite these uses, the effects of ultrasound on phase stability and resultant mechanical properties has been minimally analyzed. Here we study the impact waves play in ultrasonic welding and design an apparatus to maximize waves entering aluminum alloy samples. Aluminum 2139 and 7050 are used because they are precipitation strengthened by metastable phases so temperature change, and the corresponding phase stability, can greatly impact their strength. Results suggest that the ultrasonic welder primarily imposes a localized temperature spike due to friction, averaging over 200°C in a few seconds, which generally lowers the Vickers hardness due to coarsening or even dissolution of strengthening precipitates. Conversely, the new design increases the Vickers hardness by up to 30% over the initial hardness of approximately 63HV for aluminum 2139 and 83HV for aluminum 7050, respectively, while only increasing the temperature by an average of approximately 10°C. This new design was unable to achieve peak hardness, but the strengthening it achieved in …