The aim of this work is to study the effects of the coating process (normally applied for cementless total hip replacement (THR)) on the fatigue resistance of a titanium substrate. THR is rapidly being accepted as the surgery for diseases of the hip-joint due to high bone-ingrowth rate in porous-type cementless implants. Mechanical failure of the femoral component after total hip arthroplasty is not a common occurrence, but fractures of femoral stems after hip arthroplasty have been described. Generally the factors that predispose to this form of stem failure include excessive patient weight, high levels of physical activity, deficient osseous support, malposition or loosening of the stem, the presence of a stress-riser, and reduced cross-sectional area within the stem. It is well known that the use of titanium plasma spraying coating process reduces the fatigue resistance of the substrate. So, in order to understand the mechanism behind the coating process that decreases the fatigue resistance of the implants, an air-developed coating (Ti-APS) and one formed in a controlled atmosphere (Ti-VPS) were considered, since they are most commonly used to coat hip stems. Moreover, this work is aimed to understand the influence of the sandblasting process, here considered as a treatment preceding the coating, on the fatigue resistance of the substrate; in this regard, the most widely employed sand typologies were examined. Subsequently, the effects of the most representative parameters of the plasma spray process on the fatigue resistance were analysed; the sandblasting process, the plasma and the coating powder were taken into consideration. Fatigue resistance studies were performed by means of two rotating bending fatigue testing machines. Moreover, typical metallographic analyses (thickness, porosity and roughness examination) were carried out, complemented by morphological analyses both on the primary crack surface and on the cross-sectional area of the specimens, which underwent fatigue failure.
Lo scopo di questa tesi è di studiare gli effetti del processo di coating sulla resistenza a fatica di un substrato di titanio. In questa tesi sono stati presi in considerazione un coating sviluppato in aria (Ti-APS) e uno sviluppato in atmosfera controllata (Ti-VPS) i due maggiormente utilizzati per rivestire steli di protesi d’anca. Lo studio è rivolto anche a capire come la sabbiatura (utilizzato come trattamento precedente al rivestimento) influenzi prima del rivestimento la resistenza a fatica del substrato considerando le tipologie di sabbia maggiormente utilizzate per il rivestimento di steli di protesi d’anca. Successivamente sono stati analizzati gli effetti che i singoli parametri maggiormente rappresentanti del processo di plasma spray hanno sulla resistenza a fatica. I singoli parametri considerati sono stati: la sabbiatura, il plasma e la polvere la valutazione della resistenza a fatica è stata fatta con due macchine a flessione rotante. Oltre alle analisi a fatica sono state fatte le classiche analisi metallografiche di spessore, porosità, rugosità più delle analisi morfologiche al SEM sia sulla primary crack surface che sulla cross-sactional area dopo che il provino, rotto a fatica, è stato tagliato in sezione.
Driving factors on fatigue resistance for titanium plasma sprayed coated samples
VENTUROLI, ANDREA
2018/2019
Abstract
The aim of this work is to study the effects of the coating process (normally applied for cementless total hip replacement (THR)) on the fatigue resistance of a titanium substrate. THR is rapidly being accepted as the surgery for diseases of the hip-joint due to high bone-ingrowth rate in porous-type cementless implants. Mechanical failure of the femoral component after total hip arthroplasty is not a common occurrence, but fractures of femoral stems after hip arthroplasty have been described. Generally the factors that predispose to this form of stem failure include excessive patient weight, high levels of physical activity, deficient osseous support, malposition or loosening of the stem, the presence of a stress-riser, and reduced cross-sectional area within the stem. It is well known that the use of titanium plasma spraying coating process reduces the fatigue resistance of the substrate. So, in order to understand the mechanism behind the coating process that decreases the fatigue resistance of the implants, an air-developed coating (Ti-APS) and one formed in a controlled atmosphere (Ti-VPS) were considered, since they are most commonly used to coat hip stems. Moreover, this work is aimed to understand the influence of the sandblasting process, here considered as a treatment preceding the coating, on the fatigue resistance of the substrate; in this regard, the most widely employed sand typologies were examined. Subsequently, the effects of the most representative parameters of the plasma spray process on the fatigue resistance were analysed; the sandblasting process, the plasma and the coating powder were taken into consideration. Fatigue resistance studies were performed by means of two rotating bending fatigue testing machines. Moreover, typical metallographic analyses (thickness, porosity and roughness examination) were carried out, complemented by morphological analyses both on the primary crack surface and on the cross-sectional area of the specimens, which underwent fatigue failure.| File | Dimensione | Formato | |
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Andrea Venturoli -tesi-.pdf
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Descrizione: DRIVING FACTORS ON FATIGUE RESISTANCE FOR TITANIUM PLASMA SPRAYED COATED SAMPLES
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https://hdl.handle.net/10589/151127