"Ásbrúarsvell" (iridium, Ir 77), "keisaramálmur" and "hrapvottssilfri"

 Iridium, the most corrosion-resistant metal known, the "noblest" of metals in chemical sense, the  "emperor-metal" (keisaramálmur), because it resist "kóngavatn" (king's water, aqua regia, the strongest acid so called because it disolves the "king of metals" gold), can be named after the many colours of its salts, which was the orgin of the international name. And it can be done with a "poetic kenning"! Iridium derives from "iris" (rainbow). Irdidescence can be expressed by the adjective "lithverfur" or "róf-", "rófrænn" (in "rófsjá" (spectroscope), but could be used as a prefix too, expressing "colour-variety". And last but certainly not least we have the old poetic kenning "ásbrú", the bridge of the Aesir, which was a rainbow.  For the second part of the name we can take an old poetic name for "silver": "svell" (gleaming ice-layer): "mundar svell" (mund (hand), "mundar-' (of the hand) + svell,  the "gleaming ice layer of the hands, silver) or "fetils svell" (the gleaming sword).  Iridium is a platinum-group metal and the name "platina" is a Spanish diminutive of "plata" (silver). Iridium is silvery-white so the use of "svell" in a kenning-name for the "keisaramálmur" is appropriate "ásbrúarsvell": So three words are possible for iridiu: keisaramálmur, ásbrúarsvell and hrapvottssilfri, because iridium is the "witness of the giant space rock that impacted on Earth thereby killing  the dinosaurs.  A small layer of iridium in a layer that was 66 million years old was found all around the planet, which can only be of meteoric origin. Iridium is the "impact-witness element".

Tímaguðsefni (titanium), léttjerni, forguðaglit or korneskaefni

 1) Tímaguðsefni

The name "titanium" was given by Martin Klaproth, in accordance with his views on chemical nomenclature in the counter-flow of the French chemical school, where they tried to name the element by its chemical properties. Since the German researcher himself noted the impossibility of determining the properties of a new element only by its oxide, he chose a name for it from mythology, by analogy with uranium that he had previously discovered.  

It is, therefore, reasonable to base the Icelandic on the international word.  Because there's no Icelandic word for this name of deities, and a translation of the German "Himmerstürmer" with addition of "-efni" would generate a word that is way to long.  An alternative way is naming the element after the leader of the Titans, Kronos, the god of time. This results into the word "Tímaguðsefni", of which the first two characters coincidentially are the same as the element's symbol.  

2) Léttjerni

Titanium is well known for its combination of lightness and strenght and is used iron-alloys.  It is a member of the so-called "iron-group of transition metals".  I propose the ending -jerni for these elements.  Some might say that "-jerni" sounds like a member of the "ferromagnetic triad" (iron, cobalt and nickel). But that depends which word you suffix.  The construction "léttjerni" suggest something that is lighter than iron, so this metal can't belong to the ferromagnetic triad.  Using "léttjerni" for iron consisting of the lightest stable isotop would be terminological illogical. Scandium is often excluded form the "iron-group of transition metals because it belongs to the "rare-earth elements". For that reason "léttjerni" could be used for titanium.

3) Forguðaglit

The Titans were the 12 Gods that preceded the 12 Olympians and have become a symbol for "the elder gods", the predecessing family of Gods: Fornguða- or Forguða- + glit (metallic lustre): Forguðaglit

4) Korneskaefni (Cornium)

Named after Cornwalls, because that's where titanium was discovered. Many elements are named after the countries or regions, where they were discovered, in this case "Cornwalls".