Adriano Gonçalves dos Reis

Effect of Plasma Nitriding on Creep Behavior at 550 °C of a Maraging Steel (300 Grade) Solution Annealed

The objective of this work is to evaluate creep behavior of a maraging steel (300 grade) solution annealed before and after superficial treatment of plasma nitriding. Creep tests were conducted on a standard creep machine at stress range of 200 to 500 MPa at 550°C. Samples with a gage length of 18.5 mm and a diameter of 3.0 mm were used for all tests. Creep parameters are determined and a comparative analysis is established with the results gotten from the alloy with and without plasma nitriding. Maraging 300 steel plasma nitrided has showed a similar creep behavior compared with the same alloy without superficial treatment, with creep rate and stress exponent results very close to the material only solution annealed. This result can be associated with the strong impact of reversion of martensite to austenite and overaging at this temperature and time of exposure that minimizes the benefits of a superficial treatment.

Effect of Simultaneous Plasma Nitriding and Aging Treatment on the Microstructure and Hardness of Maraging 300 Steel

Simultaneous nitriding and aging heat treatment of maraging 300 steel was carried out inside a DC-pulsed plasma nitriding reactor. A single heat treatment cycle was done, as the plasma nitriding and age hardening processes occur at the same ranges of temperatures and times. Samples of maraging 300 steel, in the solution annealed and solution annealed and aged conditions, were tested. Plasma nitriding and aging, carried out at 480 °C for 3 h, increased the surface hardness up to 1140 HV, producing case depths of 50 μm since e-Fe3N and γ′-Fe4N nitrides were formed in the hardened surface layer. It is observed that the microstructure of the core material remains unaltered as the typical martensite plate-like microstructure of maraging steels. The core hardness of solution annealed samples increased from 331 to 597 HV after the plasma nitriding treatment proving the possibility of nitriding and aging at the same treatment cycle. The pre-aged samples did not show any overaging or martensite reversion to austenite after the simultaneous plasma nitriding and aging treatments, that could be showed by the core hardness of 620 HV and can be related to the time of total aging exposure of 6 h, including pre-aging and plasma nitriding.

A dilatometric study of the continuous heating transformations in maraging 300 steel

Dilatometric study in maraging 300 steel was carried out to study the effect of heating rate on precipitation of intermetallic phases and martensite to austenite transformation. Solution annealed material were subjected to controlled heating-holding-cooling cycles. The martensite to austenite transformation splits into two steps at lower heating rates. The first step enhanced by slow heating rate, occurs through a diffusion process, while the second step, enhanced by a fast heating rate, occurs though a shear process. The extent of precipitation decreases with heating rate, suggesting that precipitation occurs primarily by a diffusional process.

Comparation between Pulsed Nd:YAG Laser Superficial Treatment and Ceramic Coating in Creep Test of Ti-6-4V Alloy

The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatment of pulsed Nd:YAG laser and ceramic coating in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190oC by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of pulsed Nd:YAG laser and ceramic coating was submitted to creep tests at 600°C and 125 at 319 MPa, under constant load mode. In the Nd:YAG pulsed laser treatment was used an environment of 40 % N and 60 % Ar, with 2.1 W of power and 10 m/s of speed. Yttria (8 wt.%) stabilized zirconia (YSZ) with a CoNiCrAlY bond coat was atmospherically plasma sprayed on Ti-6Al-4V substrates by Sulzer Metco Type 9 MB. The obtained results suggest the laser treatment on Ti-6Al-4V alloy improved its creep resistance.

Evaluation of Creep Resistance and Superficial Study of Titanium Alloy Treated by PIII-N

The search for alloys with improved high-temperature specific strength and creep-resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. Titanium and its alloys are excellent for applications in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. However, the high affinity to oxygen is one of the main factors that limit their application as a structural material at high temperatures. Materials with adequate behavior at high temperatures and in aggressive environments have become a scientific requirement for technological and economic reasons. The goal of this work is the roughness and creep studies of the Ti–6Al–4V alloy after treatment by the nitrogen Plasma Immersion Ion Implantation (PIII-N) process. The aim of this process is the improvement of the superficial mechanical properties of the Ti–6Al–4V alloy. The selected alloy after ionic implantation process by plasma immersion was submitted to creep tests in 600 °C at 250 and 319 MPa. The techniques used in this work were Auger spectroscopy, Atomic Force microscopy (AFM), X ray, Raman spectroscopy and creep testing. The results show the significant increase of material resistance, it can be used as protection of oxidation in high temperatures applications.

Hot Tensile Behavior and Fracture Characteristics of a Plasma Nitrided Maraging 300 Steel

The influence of plasma nitriding of a maraging 300 steel on mechanical properties at high temperature has been studied. Samples were tensile tested at 600°C in four conditions: solution treated (MAR-S), solution treated and aged (MAR-SA), solution treated and plasma nitrited (MAR-SP) and solution treated, aged and plasma nitrited (MAR-SAP). In the same sequence, the yield strength and ultimate tensile strength increased slightly respectively from 1073 to 1189 MPa and 1174 to 1301 MPa, an increase of about 10% due to plasma nitriding. All the samples presented similar values of elongation, around 18%, but the cross section area reduction decreased significantly by plasma nitriding from ~70% for MAR-S and MAR-SA to ~45% for MAR-SP and MAR-SAP, that is an decrease of 36% in average. This decrease is attributed to brittle fracture nucleated at 50 μm thick iron nitride layer. The inner fracture surface of the tensile tested specimens was predominantly ductile presenting characteristic microcavities.

Superficial Parameters Determination of the Ti-6Al-4V Alloy Submitted to PIII Treatment in Different Times of Implantation

The advancement of technology leads to the development of new materials improving their tribology properties. It can be noticed in different areas like aerospace industry, chemical and oil that need resistant material in high temperatures and aggressive environments. In this case, it is important to think in its tribological properties, like wear, oxidation, toughness, and hardness. An effective mean, economic and with easy application is the plasma immersion ion implantation (PIII) technique. In the case of difficult shapes, the material can be equally treated. In this work, the Ti-Al-4V alloy was submitted to PIII during 2 and 3 h. The comparative analysis to determine which of which time was more efficient related to the tribological improvement measured by Auger, X-ray diffraction and wear. It will be observed images by MEV of the alloy submitted to PIII treatment.

Comparation between Laser Surface Nitriding and Nitrogen Plasma Immersion Ion Implantation (N-PIII) on Creep Behavior of Ti-6Al-4V Alloy

Titanium alloys are widely used in machine building, aircraft manufacturing, medicine, motors, chemistry, and biomedicine due to their high strength-to-weight ratio, elasticity, corrosion resistance, and biocompatibility. In particular, Ti-6Al-4V containing (α + β) structure plays a very important role in aerospace industry in the manufacturing of components such as disks and blades for aircrafts turbines and structural forgings. However, one of the major factors limiting the life of titanium alloys in service is their degradation due to gaseous environments, in particular, to environments containing oxygen at elevated temperatures during long-term use. The sensitivity of titanium alloys to high-temperature exposure is a well-known phenomenon. When titanium alloys are heated to temperatures above approximately 800oC, oxygen, hydrogen and nitrogen can penetrate into them. The penetration of these elements increases hardness and brittleness while decreasing the toughness of the alloy. Laser surface nitriding is a technique used to modify the near-surface microstructure and/or composition by melting the surface using a high-power laser beam with reactive gas as a shrouding environment, forming a nitride layer on the surface of Ti–6Al–4V to improve the alloy’s tribological and mechanical properties. The results of laser gas nitriding of Ti–6Al–4V showed a significant increase of microhardness and enhanced erosion resistance significantly compared with untreated Ti–6Al–4V, since the nitride layer acts as a diffusion barrier for inward oxygen diffusion into the alloy, reducing the contribution of oxygen dissolution in the substrate to the total mass gain. Other important technique that was developed for the beneficial modification of surface sensitive properties is Nitrogen Plasma Immersion Ion Implantation N-PIII. A sample is immersed in plasma and subjected to negative high-voltage pulses. In the electrical field, the ions are accelerated to high energies and incorporated into the sample. Enhancing of the hardness and wear process of the materials due to the N-enriched layer caused by diffusion of N in the sample at PIII process can be expected. Both techniques provide an improvement in the creep resistance. The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatments of laser nitriding and Nitrogen Plasma Immersion Ion Implantation N-PIII in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190 oC by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of laser nitriding and N-PIII was submitted to creep tests at 600 oC in the stress of 250 MPa and 319 MPa, under constant load mode. The creep parameters are determined and a comparative analysis is established with the results gotten from the alloy with both treatments. The laser nitrided has showed an improved creep behavior compared with the same alloy with N-PIII coating, with a reduction in the creep rate and increasing the creep lifetime.