An electrochemical and X-ray diffraction study has been conducted on the formation of lead dioxide deposits on platinum, from nitric acid solutions, as a function of potential and temperature. It has been shown that these parameters strongly influence the morphology and electrocatalytic activity of the <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">PbO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>PbO2 films. The electrodeposition process is satisfactorily described by an electrochemical, chemical, electrochemical mechanism: (i) <mml:math display="inline"><mml:msub><mml:mo>H</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>O</mml:mo><mml:mo>→</mml:mo><mml:msub><mml:mo>OH</mml:mo><mml:mrow><mml:mi mathvariant="normal">ads</mml:mi></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:msup><mml:mo>H</mml:mo><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>+</mml:mo><mml:msup><mml:mi mathvariant="normal">e</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:mo>;</mml:mo></mml:math>H2O→OHads+H++e−; (ii) <mml:math display="inline"><mml:msup><mml:mi mathvariant="normal">Pb</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>+</mml:mo><mml:msub><mml:mo>OH</mml:mo><mml:mrow><mml:mi mathvariant="normal">ads</mml:mi></mml:mrow></mml:msub><mml:mo>→</mml:mo><mml:mi mathvariant="normal">Pb</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mo>OH</mml:mo><mml:msup><mml:mo stretchy="false">)</mml:mo><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>;</mml:mo></mml:math>Pb2++OHads→Pb(OH)2+; (iii) <mml:math display="inline"><mml:mi mathvariant="normal">Pb</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mo>OH</mml:mo><mml:msup><mml:mo stretchy="false">)</mml:mo><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>+</mml:mo><mml:msub><mml:mo>H</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>O</mml:mo><mml:mo>→</mml:mo><mml:msub><mml:mi mathvariant="normal">PbO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:mn>3</mml:mn><mml:msup><mml:mo>H</mml:mo><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup><mml:mo>+</mml:mo><mml:msup><mml:mi mathvariant="normal">e</mml:mi><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:mo>;</mml:mo></mml:math>Pb(OH)2++H2O→PbO2+3H++e−; the second electron transfer stage and <mml:math display="inline"><mml:msup><mml:mi mathvariant="normal">Pb</mml:mi><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:math>Pb2+ diffusion control the dioxide formation in the lower and higher overpotential range, respectively. Temperature and potential (or current) are important parameters in the electrodeposition process. Depending on the potential region, the process can be kinetically or diffusion controlled. In an acid electrolyte, where mainly the <mml:math display="inline"><mml:mi>β</mml:mi><mml:mo>­</mml:mo><mml:msub><mml:mi mathvariant="normal">PbO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>β­PbO2 modification is electrodeposited, the amount of α-phase impurity increases with increasing potential in the kinetically controlled region and decreases in the diffusion controlled domain. In addition, relatively low electrodeposition potentials and high temperatures favor an increase of the crystallite size with preferred crystallographic orientation for both α- and <mml:math display="inline"><mml:mi>β</mml:mi><mml:mo>­</mml:mo><mml:msub><mml:mi mathvariant="normal">PbO</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>β­PbO2 modifications. The temperature of the growth solution affects the crystallinity of the resulting oxide deposits and has a marked effect on their performance as anodes in processes at high positive potentials such as ozone generation. © 2002 The Electrochemical Society. All rights reserved.

In this study, hardfacing and a flux-cored/self-shielded powder wire of the FCAW-S-90G13N4 type was employed to produce and investigate the deposits of high-manganese steel. The effects of high-frequency mechanical impact (HFMI) treatment on the microstructure, hardening, and scratch resistance of the deposits were studied to evaluate and predict the impact wear resistance of the hardfacing deposits under controlled impact load conditions. As observed by XRD, SEM, and nanoindentation, the microstructure of deposited metal comprised a soft austenite matrix, dispersed hard carbides, and an ε phase (~26 vol.%). The wear resistance is thus not controlled by carbides alone but arises from the synergistic action of a hard carbide network within a ductile matrix. HFMI resulted in twinning, an increase in dislocation density, a grown volume fraction of ε (>60%) and α′-martensite. The interaction between twins, martensites, and dislocations provides a double/triple increase in microhardness (from HV_0.2 = 2.78 GPa to HV_0.2 = 6–7.69 GPa). After HFMI, scratch tests showed lower restored depths of scratch tracks and a 36–68% deceleration in the wear rate regarding those of the initial deposit. The underlying wear mechanisms were assessed accounting for the SEM observations of the scratch track morphologies and a ‘counterbody penetration vs. shear stresses ratio’ map. The initial plastic deformation-related mechanism (wedge/pile-up formation) changed by HFMI to ploughing. The obtained results allow one to evaluate and predict the impact wear resistance of the hardfacing deposits under controlled impact load conditions.